IRLF 


B    3 


RAILWAY  SIGNALING 

A  COMPREHENSIVE  TREATISE  ON  MODERN 
METHODS  OF  RAILWAY  SIGNALING,  COV- 
ERING PRINCIPLES  OF  OPERATION 
AND  TYPES  OF  APPARATUS 


Written  by  a  Staff  of  Expert 
Signal  Engineers 


Published  by 

THE  ELECTRIC  JOURNAL 

42 #4  Sixth  Avenue 

Pittsburg,  Pa. 

1908 


Copyright,  1908, 

by 
THE  ELECTRIC  JOURNAL 


Preface 

The  lack  of  any  adequate  literature  on  the  subject  of  Railway 
Signaling  was  called  to  the  attention  of  the  editors  of  THE  ELECTRIC 
JOURNAL  about  two  years  ago,  when  an  attempt  .was  made  to  secure 
some  information  on  the  subject.  On  looking  over  such  material  as 
was  available  it  was  found  that  there  were  no  publications  giving  a 
logical  treatment  of  the  subject  in  the  present  state  of  the  art.  It  was, 
therefore,  thought  quite  worth  while  to  undertake  the  publication  of 
a  comprehensive  series  of  articles  along  this  line.  An  outline,  cover- 
ing the  subject,  was  prepared  and  permission  was  finally  obtained 
from  the  management  of  The  Union  Switch  &  Signal  Company  to 
have  a  number  of  their  engineers  prepare  a  series  of  articles  for  the 
JOURNAL.  In  this  way  it  has  been  possible  to  obtain  at  first  hand  the 
latest  and  most  authoritative  information  from  men  who  are  making 
a  life  study  of  the  subjects  which  they  treat  and  who  are  closely  in 
touch  with  the  latest  developments  in  signaling.  In  describing  the 
various  principles  of  operation  and  types  of  apparatus,  many  of 
which  appear  very  complicated,  especially  in  installations  of  large 
size,  the  effort  has  been  to  make  the  reading  pages  and  illustrations 
easily  understood  by  the  average  reader.  In  many  cases  special  il- 
lustrations have  been  prepared  to  show  the  operation  of  apparatus 
in  principal  rather  than  in  detail. 

It  is  believed  that  the  following  pages  will  prove  of  much  value 
to  all  who  are  interested  in  railway  work. 

The  following  men,  engineers  of  The  Union  Switch  &  Signal 
Company,  are  entitled  to  much  credit  for  the  painstaking  manner  in 
which  they  have  handled  their  particular  subjects:  T.  George  Will- 
son,  Interlocking  Engineer;  W.  H.  Cadwallader,  Signal  Engineer; 
John  D.  Taylor,  Assistant  Electrical  Engineer;  T.  H.  Patenall,  Sig- 
nal Engineer;  W.  E.  Foster,  Engineering  Assistant  to  the  General 
Manager;  J.  B.  Struble,  Assistant  Electrical  Engineer. 

Pittsburg,  Pa.,  June,  1908. 


256806 


Reprinted  from  a  series 
of  articles  on 

RAILWAY  SIGNALING 

Published  during  the 
year  1907 

in 

©I|p  Elertrtr  Journal 

A  monthly  magazine  dealing 
with  subjects  of  interest  to  the 
engineering  fraternity  in  gen- 
eral, and  to  those  in  the  elec- 
trical field  in  particular.  Its 
staff  of  contributors  consists 
almost  entirely  of  engineers 
engaged  in  active  engineering 
work  ::  ::  ::  ::  ::  ::  :: 


TABLE   OF   CONTENTS 

CHAPTER  I MECHANICAL  INTERLOCKING 7-18 

Types  of  Machines — Method  of  Signaling  a  Plan  of 
Tracks — Form  of  Signals — Details  of  Construction. 

CHAPTER  II.  .ELECTRO- PNEUMATIC  INTERLOCKING.  .  19-37 

General  Principles  —  Principal  Items — The  Power 
Plant — The  Interlocking  Machine — The  Operating  Tower 
Pneumatic  and  Electric  Connections — Switches,  Locks, 
Signals — Auxiliary  Appliances. 

CHAPTER  III ELECTRIC  INTERLOCKING 38-52 

Development  of  Electric  Interlocking — Switch  and 
Lock  Mechanism— Safety  Controller  for  Switches. 

CHAPTER  IV. THE  ELECTRIC  TRAIN  STAFF  SYSTEM. 53-71 

Development — Application  of  Train  Staff  System 
— Principal  Advantages  of  the  Electric  Train  Staff 
System — Absolute  Staffs  and  Staff  Instruments — Per- 
missive Feature — Control  of  Signals — Switch  Locking 
—Siding  and  Junction  Instruments — Pusher  Engine 
Attachments. 

CHAPTER  V AUTOMATIC  BLOCK  SIGNALING.  .  .  .  72-80 

Definitions  and  Classifications — Early  Block  Systems 
— Automatic    Block    Signals — Length    of    Blocks — Sema- 
phores  on    Separate    Posts — Semaphores   on   Same    Posts 
-Three  Position  Signals — Overlap  Systems— Construction. 

CHAPTER  VI.  .AUTOMATIC  BLOCK  SIGNALING — DIRECT 

CURRENT 81-87 

Systems  of  Circuits — Relays — Operating  Mechanism 
—Cost. 

CHAPTER  VII .  .AUTOMATIC  BLOCK  SIGNALING- 
ALTERNATING  CURRENT 88-95 

General  Signal-Rail  System — Application  of  the 
Single-Rail  System — Signaling  on  Steam  Roads. 

CHAPTER  VIII.  .AUTOMATIC  BLOCK  SIGNALING- 
ALTERNATING  CURRENT 96-100 

Double-Rail  Return  System— Direct-Current  Train 
Propulsion — Alternating-Current  Train  Propulsion. 

CHAPTER   IX. THE  LANGUAGE  OF  FIXED  SIGNALS.. 101-108 


CHAPTER  I 

MECHANICAL  INTERLOCKING 

AN  interlocking  plant  consists  of  a  group  of  levers  concen- 
trated at  a  central  point  for  operating  certain  switches  and 
signals,  and  so  arranged  as  to  interlock  such   levers  and 
make  it  impossible  to  give  clear  signals  for  conflicting  routes.     The 
advantages  derived  therefrom  are  safety,  facility  of  operation  and 
saving  in  cost  of  manual  labor  employed. 

It  is  the  purpose  of  this  article  to  give,  as  briefly  as  possible,  a 
general  outline  of  what  is  accomplished  by  interlocking,  the  manner 
in  which  the  work  is  done,  and  the -construction  of  a  particular  type 
of  machine. 

TYPES   OF    MACHINES 

As  has  been  intimated,  various  types  are  in  use,  and  they  may 
be  divided  into  classes  as  follows:  Mechanical,  hydro-pneumatic, 
electro-pneumatic,  pneumatic,  and  electric. 

Each  style  of  machine  is  known  by  the  kind  of  power  utilized  to 
perform  the  various  functions  for  which  it  was  designed,  and  as  all 
were  designed  for  the  purpose  of  doing  a  certain  kin'd  of  work,  a 
description  of  the  original  (mechanical)  machine,  will  give  not  only 
the  method  of  operation  peculiar  to  itself,  but  also  a  general  idea  of 
the  principle  of  interlocking  as  used  in  all  machines. 

An  interlocking  machine  may  be  small  in  size,  that  is,  may  have 
but  few  levers,  sufficient  to  properly  protect  a  single  track  grade 
crossing ;  or  it  may  be  to  take  care  of  a  crossover  between  the  tracks 
of  a  double  track  road;  or  to  protect  a  junction  point  where  two 
single  track  roads  converge.  Or,  on  the  other  hand,  the  machine 
may  be  a  large  one,  with  many  levers,  sufficient  to  properly  handle 
a  grade  crossing  where  several  roads  cross  other  roads,  and  per- 
haps having  interchange  tracks;  or,  it  may  be  for  handling  a  large 
classification  yard,  a  large  passenger  terminal,  or  a  combination  of 
any  of  the  above.  Therefore,  the  size  of  machine  depends  entirely 
upon  the  arrangement  of  tracks  at  the  point  to  be  protected. 

METHOD   OF    SIGNALING   A    PLAN    OF   TRACKS 

When  it  is  desired  to  install  an  interlocking  plant,  the  first  thing 
is  to  have  a  plan  of  tracks,  which  is  then  signalled  up,  that  is,  all 


8 


^RAILWAY  SIGNALING 


the  switches  to  be  operated  are  noted ;  the  derails,  signals,  tower, 
and  run  of  connections  are  located;  the  size  of  machine  and  func- 


tions  of  each  lever  are  determined;  and  a  diagram  of  the  leadout 
made,  as  illustrated  by  Fig.  i.     From  the  signalled  plan,  a  locking 


RAILWAY  SIGNALING  9 

sheet  is  then  made,  that  is,  the  proper  interlocking  to  be  done  be- 
tween levers  is  determined,  as  illustrated  by  the  locking  sheet  in 
Fig.  5.  From  the  locking  sheet,  a  dog  sheet  is  made,  this  being  a 
diagram  which  shows  the  arrangement  of  the  interlocking  parts  as 
they  are  to  be  placed  in  the  machine.  This  is  illustrated  by  the  dog 
sheet  in  Fig.  5. 

The  plan,  as  shown  on  Fig.  I,  is  a  typical  layout  of  tracks, 
showing  a,  grade  crossing  protected  by  derails,  and  a  siding  connect- 
ed with  one  of  the  main  tracks  by  a  crossover.  At  each  switch  or 
derail  a  signal  is  located  to  govern  movements  over  the  point  where 
the  tracks  intersect.  The  numbers  shown  at  each  switch,  derail,  sig- 
nal, etc.,  mean  that  that  particular  switch,  derail,  signal,  etc.,  is  to  be 
operated  by  a  lever  in  the  machine  having  the  same  number.  That 
is,  lever  I  will  control  signal  i,  lever  p  derail  p,  etc.  By  referring 
to  the  scheme,  it  will  be  found  that  eighteen  levers  will  be  required 
to  operate  this  plant,  but  as  mechanical  machines  are  built  up  of  four 
lever  sections,  a  machine  will  be  used  having  eighteen  working  levers 
and  two  spare  spaces,  the  latter  being  available  for  levers  in  case  it 
be  necessary  to  make  an  addition  to  the  plant  at  some  future  time. 

When  no  movements  are  being  made  over  the  crossing,  all  de- 
rails are  open,  the  switch  on  the  siding  set  for  the  stub  end,  and  all 
signals  are  in  the  horizontal  (danger;  stop)  position,  and  when  in 
such  position,  they  are  known  as  being  normal  and  the  levers  in  the 
machine  are  normal  also.  When  a  derail  is  closed,  a  switch  thrown, 
or  a  signal  cleared,  they  are  then  known  as  being  in  the  reverse  posi- 
tion, and  the  lever  by  which  the  operation  is  performed  is  then  also 
known  as  being  in  the  reverse  position. 

When  a  movement  is  desired  over  any  one  of  the  tracks,  it  is 
necessary  to  set  all  switches  and  derails  in  the  right  position  for  such 
movement,  then  lock  them  in  such  position,  after  which  the  signal 
governing  traffic  over  that  particular  track  may  be  cleared.  Under 
the  head  of  "Manipulation"  in  Fig.  I,  is  a  table  showing  just  what 
levers  are  to  be  reversed  to  allow  movements  over  the  various  routes. 
For  example,  in  order  to  allow  a  train  to  go  from  A  to  D,  levers 
13-11-9-8-2  and  i  must  be  reversed  in  the  order  named,  and  the  last 
lever  reversed  locks  all  of  the  preceding  ones.  The  closing  of  either 
derail  in  the  route  will  lock  the  derails  of  conflicting  routes  normal, 
they  in  turn  will  hold  the  signals  normal.  Therefore  it  will  be  seen 
that  where  two  or  more  routes  conflict,  the  signals  of  but  one  can 
be  cleared. 


io  RAILWAY  SIGNALING 

SWITCHES   AND  DERAILS 

A  switch  is  used  to  deflect  traffic  from  one  track  to  another.  A 
derail  is  in  reality  a  switch,  and  is  also  used  for  deflecting  traffic,  but 
not  from  one  track  to  another,  for  as  its  name  implies,  its  purpose 
is  to  derail,  or  deflect  from  the  rails  onto  the  ties,  or  ground,  or  into 
some  short  track  or  obstruction,  in  order  to  stop  traffic  if  the  signal 
be  disregarded.  Nos.  9-12-13-14  in  Fig.  I  represent  derails.  They 
operate  in  such  a  way  that  if,  for  any  reason,  an  engineer  attempts 
to  take  his  train  over  a  crossing  when  the  signal  governing  the 
movement  is  normal  (stop)  his  train  will  be  derailed,  and  as  the 
derails  are  located  300  feet  from  the  crossing,  the  train  would  not 
reach  the  tracks  of  the  other  road,  (which  may  be  occupied  by  an- 
other train),  even  though  it  may  have  been  moving  at  high  speed 
before  leaving  the  rails.  Although  derails  will  accomplish  this,  it  is 
not  expected  or  desired  that  this  should  occur,  and  it  very  rarely 
happens  for  the  reason  that,  if  an  engineer  knows  his  train  will  be 
derailed  if  he  attempts  to  pass  a  signal  at  danger,  he  will  be  very 
careful  to  stop  at  the  signal. 

THE  DETECTOR  BAR 

At  each  switch  is  a  bar  which  lies  against  the  outside  of  the  rail, 
and  is  so  adjusted  that  the  top  of  the  bar,  when  in  the  normal  posi- 
tion, is  three-eights  of  an  inch  below  the  top  of  the  rail.  This  is 
what  is  known  as  a  detector  bar,  and  works  in  conjunction  with  the 
lock  on  a  switch,  so  that  when  a  movement  is  being  made  over  a 
switch,  the  wheels  will  prevent  the  bar  from  being  raised,  thus  pre- 
venting the  leverman  from  unlocking  the  switch  when  a  train  is 
passing  over  it.  Before  a  train  movement  can  be  made,  all  switches, 
after  having  been  set  in  the  proper  position,  must  be  locked.  This 
is  done  by  a  bolt  or  dog  being  thrust  through  a  notch  or  hole  in  a 
bar  connected  to  the  points  of  the  switch.  If  for  any  reason  the 
switch  points  do  not  go  to  the  proper  place  when  the  lever  by  which 
the  switch  is  operated  is  thrown,  it  is  obvious  that  the  bolt  or  dog 
cannot  be  thrust  through  the  bar  and  the  switch  cannot  be  locked, 
thus  indicating  to  the  leverman  that  the  switch  is  not  in  proper  posi- 
tion. 

METHOD   OF   LOCKING   SWITCHES   AND  DERAILS 

A  switch  may  be  moved  and  also  locked  by  a  single  lever. 
When  this  is  done,  a  mechanism  called  a  switch  and  lock  movement 


RAILWAY  SIGNALING 


II 


12  RAILWAY  SIGNALING 

is  used,  it  being  located  opposite  the  switch.  When  actuated  by  a 
lever  in  the  machine,  the  first  part  of  the  stroke  unlocks  the  switch, 
the  mid-stroke  throws  it,  and  the  last  part  of  the  stroke  locks  it. 
Thus  the  switch  is  locked  either  normal  or  reversed,  depending  upon 
the  position  of  the  lever.  When  such  a  device  is  used,  on  main 
tracks,  the  signals  governing  movements  over  such  tracks  are  also 
made  to  lock  the  switch  by  means  of  what  is  called  a  bolt  lock,  which 
makes  it  impossible  for  a  signal  to  be  cleared  if  for  any  reason  the 
switch  is  not  in  the  proper  position.  Fig.  2  illustrates  a  switch  and 
lock  movement  with  bolt  lock  applied  to  a  derail. 

While  some  roads  use  switch  and  lock  movements  on  main 
tracks,  most  roads  use  them  only  for  the  siding  end  of  cross-overs, 
or  for  derails  on  unimportant  sidings,  preferring  the  use  of  a  sepa- 
rate lever  to  operate  the  locks  on  main  line  switches.  When  a  sepa- 
rate lever  is  used,  the  lock  is  called  a  lacing  point  lock,  getting  its 
name  from  the  fact  that  originally  a  switch  was  locked  only  when 
traffic  was  to  be  given  the  right  of  way  in  the  direction  facing  the 
switch  point,  but  present  practice  is  to  lock  all  switches  whether 
traffic  be  facing  the  points  or  trailing.  Some  roads  also  use  a  bolt 
lock,  operated  by  the  signal,  as  an  additional  precaution,  even  when 
a  switch  is  locked  by  a  facing  point  lock.  Fig.  3  shows  a  facing 
point  lock  with  bolt  lock  applied  to  a  switch. 

FORM    OF   SIGNALS 

Referring  again  to  Fig.  i,  it  will  be  noticed  that  all  signals  lo- 
cated on  main  tracks  are  shown  high  and  the  two  located  on  siding 
are  low,  it  being  the  general  practice  to  use  high  signals  for  main 
tracks,  in  the  direction  of  ordinary  traffic,  and  low  or  dwarf  signals 
for  movements  on  or  out  of  sidings  or  against  traffic  on  main  tracks. 
A  high  signal  with  square  end  blade  is  called  a  home  signal ;  with 
the  end  of  blade  notched,  it  is  known  as  a  distant  signal.  A  distant 
bla'de  horizontal  means  caution,  that  the  home  signal  in  advance  of 
it  may  be  at  danger.  When  a  distant  blade  is  inclined,  it  means 
clear,  and  indicates  that  the  home  signal  is  clear  also.  Therefore, 
if  an  engineer  approaches  a  distant  signal  and  finds  it  at  clear,  he 
may  proceed  at  high  speed,  knowing  that  the  main  line  route  has 
been  set  up  and  ready  for  him  to  proceed  without  a  stop ;  but  if  he 
finds  the  distant  at  caution,  he  must  approach  the  home  signal  ex- 
pecting to  find  it  at  danger. 

A  dwarf  signal  with  the  blade  horizontal  indicates  danger,  stop ; 
with  the  blade  inclined,  indicates  clear,  proceed  slowly,  as  move- 


RAILWAY  SIGNALING 


14  ;      RAILWAY  SIGNALING 

ments  on  or  out  of  a  siding  or  against  traffic  on  main  tracks  neces- 
sarily should  be  made  cautiously. 

DETAILS   OF    CONSTRUCTION 

The  dotted  lines  in  Fig.  I  leading  from  the  tower  along  the 
tracks,  indicate  the  location  of  the  pipe  and  wire  connections  from 
the  machine  to  the  various  switches,  signals,  etc.,  these  connections 
being  shown  in  detail  under  the  heading  Leadout.  In  the  leadout 
each  full  line  represents  a  single  line  of  pipe,  and  each  dotted  line 
represents  two  wires,  each  line  having  a  number  corresponding  to 
its  operating  lever.  Pipe  lines  are  supported  by  roller  carriers  on 
wood,  iron  or  concrete  foundations,  placed  every  seven  feet,  and 
when  such  lines  are  over  fifty  feet  long,  a  compensator  (to  take  care 
of  expansion  and  contraction  due  to  changes  in  temperature)  is 
used.  Wire  lines  are  supported  in  the  same  manner  as  pipe,  except- 
that  the  carriers  are  placed  every  twenty-one  feet,  and  compensation 
is  usually  taken  care  of  by  adjusting  screws  located  in  the  tower. 

The  letters  ZZ  on  the  leadout  shown  in  Fig.  i  represent  the 
point  on  Fig.  4,  where  the  vertical  cranks  and  wheels  are  located, 
and  through  which  connection  is  made  to  the  machine.  In  the  ma- 
jority of  cases  machines  are  located  so  as  to  be  operated  from  the 
second  floor  of  a  tower,  because  it  is  desirable  that  a  lever  man  shall 
have  a  good  view  of  the  tracks  and  signals.  Some  machines  are 
built,  however,  to  be  operated  from  the  ground  floor. 

All  machines  have  the  levers  numbered  consecutively,  begin- 
ning with  the  left-hand  end  facing  the  levers.  Mechanical  machines 
may  be  'divided  into  two  classes,  those  having  lever  locking  and 
those  having  latch  (or  preliminary)  locking.  The  levers  of  all  ma- 
chines are  provided  with  latches,  the  purpose  of  which  is  to  keep  the 
levers  in  the  normal  or  reverse  position.  In  a  machine  having  lever 
locking,  the  latch  is  used  for  no  other  purpose  than  that  stated  above, 
the  interlocking  parts  being  actuated  only  by  changing  the  position 
of  the  lever  itself,  which  necessarily  brings  great  strain  on  the  lock- 
ing parts,  when  an  attempt  be  made  to  throw  a  lever  when  it  is 
locked.  Therefore,  for  such  a  machine,  the  locking  parts  must  be 
made  large  and  strong.  In  a  machine  having  latch  locking,  the  latch 
is  used  not  only  for  holding  the  lever  in  the  normal  or  reverse  posi- 
tion, but  also  for  actuating  the  locking  parts.  That  is,  these  parts 
are  connected  to  and  operated  by  the  latch,  instead  of  the  lever,  thus 
permitting  lighter  construction.  As  the  raising  of  the  latch  is  a 
preliminary  step  to  the  throwing  of  a  lever,  the  locking  will  there- 


RAILWAY  SIGNALING  15 

fore  be  accomplished  before  the  lever  moves  from  its  position.  This 
will  be  more  readily  understood  by  referring  to  Fig.  4,  which  shows 
a  machine  with  the  levers  in  the  normal  position.  The  machine  il- 
lustrated is  known  as  the  Saxby  &  Farmer,  a  type  generally  used, 
not  only  because  of  the  preliminary  locking  feature,  but  also  because 
of  the  design  of  the  locking  parts.  The  parts  of  this  machine  by 


FIG.    4 — END    VIEW    OF    SAXBY    AND    FARMER    INTERLOCKING    MACHINE    WITH 
CONNECTIONS   AS  LOCATED   IN   TOWER 

which  the  interlocking  between  levers  is  accomplished,  are  known 
as  the  latch,  rocking  link,  shaft,  driver,  bar,  dogs  and  cross  locks. 
See  Fig.  4.  When  a  latch  is  raised,  a  bar  is  moved  a  certain  dis- 
tance ;  to  this  bar  dogs  are  riveted,  which  in  turn  drive  the  cross 
locks  against  other  dogs  which  are  riveted  to  bars  operated  by  other 


1 6  RAILWAY  SIGNALING 

latches.  With  a  lever  in  its  normal  position,  the  raising  of  the  latch 
gives  half  of  the  necessary  stroke  to  the  bar,  the  remainder  of  which 
is  given  by  dropping  the  latch  after  the  lever  has  been  reversed.  As 
the  same  is  true  when  throwing  a  lever  from  the  reverse  to  the  nor- 
mal position,  therefore,  no  matter  in  which  position  a  lever  stands, 
when  the  operation  of  moving  it  takes  place,  the  first  thing  to  happen 
is  the  raising  of  the  latch,  which  accomplishes  all  of  the  locking, 
then  occurs  the  movement  of  the  lever,  during  which  time  no  change 
in  the  locking  takes  place,  last,  the  dropping  of  the  latch  which  re- 
leases those  levers  which  are  to  be  thrown  next. 

Fig.  5  shows  a  locking  and  dog  sheet,  the  former  showing  just 
what  locking  is  desired,  the  latter  showing  the  arrangement  o<f  the 
locking  in  the  machine,  this  diagram  being  used  not  only  for  a  rec- 
ord, but  also  by  the  shop  men,  for  it  is  from  this  that  the  locking 
parts  are  constructed.  The  numbers  at  the  top  of  the  diagram  repre- 
sent the  levers  in  the  machine,  and  the  heavy  vertical  lines  represent 
shafts  operated  by  the  levers.  The  full  length  horizontal  lines  repre- 
sent bars,  each  being  given  a  number  by  which  it  is  known,  and  each 
to  be  operated  by  some  particular  lever,  by  means  of  a  driver,  which 
is  indicated  by  a  small  circle  where  the  lines  representing  shafts  and 
bars  intersect.  Hence  it  will  be  seen  that  lever  20  operates  bar  /p, 
lever  p  bar  8,  lever  ij  bar  18,  etc.  On  each  bar  certain  dogs  are 
riveted,  which  when  a  bar  is  moved,  drives  a  cross-lock  against  dogs 
which  are  riveted  on  othen  bars,  thus  accomplishing  certain  locking. 
To  illustrate,  notice  dog  a  which  is  riveted  to  bar  2,  the  bar  being 
operated  by  lever  2.  If  the  latch  of  lever  2  be  raised,  the  bar  will 
be  moved  to  the  right,  thus  driving  the  cross-lock  b  against  the  dog 
c.  Hence  2  reversed,  locks  17  normal,  as  required  by  the  locking 
sheet. 

The  above  is  a  very  simple  case,  and  is  called  straight  locking, 
being  a  positive  lock  between  two  levers.  The  following  is  a  more 
difficult  one.  For  example,  a  lever  to  lock  another  lever  depending 
upon  the  position  of  a  third.  Such  an  arrangement  is  shown  on  the 
dog  sheet  by  d-e-f-g-h.  It  may  be  seen  that  if  dog  d  be  moved  to 
the  right  when  dog  e  is  normal,  dog  /  may  be  moved  also,  but  if  dog 
e  first  be  moved  to  the  right,  thus  filling  the  space  between  cross- 
locks  g  and  h,  then  before  the  dog  d  can  be  moved,  dog  /  must  be 
moved,  and  when  this  is  done,  the  moving  of  dog  d  drives  the  cross- 
lock  g  against  dog  e,  and  as  this  latter  is  a  swing  dog,  through  it 
the  motion  is  communicated  to  the  cross-lock  h,  which  in  turn  is 
driven  against  dog  /,  and  holds  it  in  the  reverse  position  so  long 


RAILWAY  SIGNALING 

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as  dogs  e  and  d  are  kept  in  the  same  position.  Thus  5  reversed  locks 
ii  reversed  when  10  is  reversed,  as  required  by  the  locking  sheet. 
This  is  an  example  of  a  very  simple  case  of  special  locking.  In  large 
machines  it  often  happens  that  the  locking  between  certain  levers 
depends  upon  the  position  of  perhaps  ten  or  more  other  levers,  and 
it  is  this  feature  which  makes  the  arranging  of  the  locks,  as  well  as 
determining  what  locking  is  necessary,  quite  an  engineering  problem. 
It  very  seldom  happens  that  any  two  machines  are  locked  up  exactly 
the  same,  as  the  locking  required  depends  entirely  upon  the  number 
and  arrangement  of  tracks,  and  the  signaling  desired. 

There  are  many  special  appliances  and  attachments,  of  both  a 
mechanical  and  electrical  nature,  which  are  often  used  in  connection 
with  an  interlocking  machine  such  as  has  been  described,  but  enough 
information  has  been  given  in  this  article  to  enable  those  who  are 
unfamiliar  with  interlocking  to  understand,  in  a  general  way,  one  of 
the  methods  used  to  handle  traffic  safely  and  quickly. 


CHAPTER  II 

ELECTRO-PNEUMATIC  INTERLOCKING 

AN  interlocking  system  has  been  defined  by  the  American  Rail- 
way Association  as  "An  arrangement  of  switch,  lock  and 
signal  appliances  so  interchanged  that  their  movements  must 
succeed  each  other  in  a  pre-determined  order."  The  definition  applies 
equally  well  to  the  mechanical  and  electro-pneumatic  interlocking 
systems ;  the  latter,  however,  possesses  certain  distinct  advantages 
over  the  former,  among  the  most  important  of  which  are  the  fol- 
lowing : 

i — It  is  fifty  percent  quicker  in  operation  than  the  mechanical 
system,  and  at  least  ten  percent  quicker  than  any  other  power  ope- 
rated system  at  present  in  use,  thus  permitting  extremely  rapid  train 
movements  on  congested  tracks  such  as  large  terminals,  elevated 
lines  and  subways. 

2 — The  interlocking  machine  usually  requires  less  than  one- 
quarter  of  the  space  occupied  by  a  mechanical  machine  for  operat- 
ing the  same  number  of  switches,  locks,  and  signals,  thus  econo- 
mizing in  the  size  of  the  building  or  "tower"  containing  it. 

3 — As  the  small  operating  levers  entail  very  little  effort  on  the 
part  of  the  leverman  to  manipulate  them,  and  as  less  levers  are  re- 
quired than  in  a  mechanical  plant,  fewer  levermen  are  necessary  for 
the  operation  of  large  plants. 

4 — The  space  required  for  the  pipe  and  wire  lines  between  the 
levers  and  functions  operated  in  mechanical  plants  can  be  used  for 
other  purposes  where  electro-pneumatic  interlockings  are  installed, 
since  the  room  occupied  by  the  wire  and  cables  between  levers  and 
functions  is  comparatively  small,  and  where  necessary  these  pipes 
and  wires  can  be  placed  in  underground  conduits. 

As  an  example  of  the  foregoing  the  electro-pneumatic  inter- 
locking plant  at  the  St.  Louis  Terminal  of  the  Terminal  Railroad 
Association  of  St.  Louis  may  be  cited.  The  machine  for  operating 
this  plant  which  includes  44  double  slip  switches  with  movable  point 
frogs,  65  single  switches  and  194  signals,  is  about  44  feet  in  length 
over  all,  and  contains  only  215  levers,  of  which  33  are  not  in  use, 
being  available  for  future  additions  to  the  plant;  whereas,  a  me- 
chanical plant  to  operate  this  terminal  would  have  contained  528 
levers,  and  been  245  feet  long.  Five  levermen  on  the  busiest  shift 


20  RAILWAY  SIGNALING 

operate  the  electro-pneumatic  machine,  while  not  less  than  twenty 
men  would  have  been  required  for  a  mechanical  machine  under  sim- 
ilar conditions.  The  wires  and  compressed  air  pipes  at  the  St. 
Louis  Terminal  are  all  placed  underground,  and  are  entirely  out  of 
the  way,  while,  had  a  mechanical  plant  been  installed,  the  Terminal 
Company  would  have  had  to  purchase  considerable  extra  land  on 
which  to  run  the  connections. 

GENERAL    PRINCIPLES 

Briefly  outlined,  the  electro-pneumatic  interlocking  system  pro- 
vides for  the  operation  of  switches,  locks  and  signals  by  compressed 
air  and  their  control  by  electricity.  This  is  effected  by  applying 
pneumatic  cylinders  to  all  such  functions,  and  admitting  and  releas- 
ing compressed  air  to  and  from  these  cylinders  by  means  of  valves 
actuated  by  electro-magnets  which  are  energized  from  batteries  or 
generators  located  in  the  operating  tower,  the  circuits  being  con- 
trolled by  the  manipulation  of  the  levers  in  the  interlocking  machine. 
The  movements  of  the  switches  and  signals  are  in  turn  repeated 
back  to  the  machine  levers  through  circuit  controllers  located  at  the 
switches  and  signals  and  operated  by  them,  thus  electrically  locking 
and  unlocking  the  levers  as  the  position  of  the  switches  and  signals 
may  necessitate.  By  these  means  positive  indications  are  given  that 
the  movements  of  the  switches  and  signals  at  all  times  corre- 
spond with  the  positions  of  their  respective  levers. 

PRINCIPAL   ITEMS 

An  electro-pneumatic  interlocking  plant  includes  the  following: 

i — The  power  plant,  comprising  the  air  compressors,  cooling- 
coils  and  reservoirs,  the  electric  generators,  switchboard  and  bat- 
teries. 

2 — The  interlocking  machine,  comprising  the  operating  levers, 
the  mechanical  locking,  the  electric  circuit  controllers,  and  the  elec- 
tric locks. 

3 — The  operating  tower,  which  contains  the  interlocking  ma- 
chine and  such  other  devices  as  may  be  necessary  for  quickly  com- 
municating and  obtaining  information  from  other  points.  These 
are  usually  in  the  form  of  visible  or  audible  indicators,  telephones, 
and  telegraph  instruments. 

The  main  battery  and  electric  generators  are  frequently  located 
in  the  lower  story  of  the  tower. 


RAILWAY  SIGNALING 


21 


22  RAILWAY  SIGNALING 

4 — The  pneumatic  connections  between  the  compressing  plant 
and  the  switches  and  signals,  and  the  electric  connections  between 
them  and  the  interlocking  machine. 

5 — The  functions,  under  which  term  the  switches,  locks  and 
signals  are  generally  referred  to. 

6 — The  auxiliary  appliances,  such  as  track  circuits  for  the  auto- 
matic control  of  signals  and  locks,  gateman's  indicators,  annuncia- 
tors, etc. 

THE   POWER  PLANT 

At  practically  all  of  the  large  terminals  and  at  a  nuniDer  of 
other  places  where  electro-pneumatic  interlocking  plants  are  in  ope- 
ration, compressed  air  is  largely  used  for  other  purposes  such  as 
charging  air  brake  tanks,  cleaning  cars  and  driving  machinery. 
Consequently  the  pneumatic  power  for  the  interlocking  plant  can 
usually  be  taken  from  existing  compressors.  This  air  is  first  passed 
through  cooling  coils  having  a  sufficiently  large  radiating  surface  to 
extract  the  heat  generated  by  compression,  and  reduce  the  temper- 
ature of  the  air  to  that  of  the  atmosphere  before  it  reaches  the  main 
air  pipe.  Reservoirs  of  comparatively  large  capacity  are  placed  be- 
low these  cooling  coils.  These  serve  the  double  purpose  of  main- 
taining a  reserve  supply  of  air,  should  the  compressor  be  stopped 
for  a  short  time,  and  of  collecting  the  moisture  which  has  been  con- 
densed by  the  cooling  coils.  After  leaving  the  cooling  coils  the  air 
is  conveyed  by  main  pipes  of  from  two  to  four  inches  in  diameter 
through  the  entire  system.  The  pipes  are  usually  so  arranged  as  to 
provide  two  paths  by  which  the  air  can  reach  each  switch  or  signal 
so  that,  in  case  of  the  breakage  or  stoppage  of  any  pipe,  the  plant 
can  continue  to  operate.  Suitable  expansion  joints  are  provided  to 
allow  for  variation  in  temperature. 

From  the  main  pipes,  the  air  is  conducted  in  smaller  branch 
pipes  to  the  switches  and  signals  and  at  the  end  of  each  branch  an 
auxiliary  reservoir  is  located  to  catch  whatever  moisture  may  have 
escaped  the  main  reservoirs.  The  main  and  auxiliary  reservoirs  are 
provided  with  cocks  so  that  the  water  may  be  blown  off  from  time 
to  time. 

The  electrical  power  equipment  usually  consists  of  two  smal] 
generators,  driven  by  engines  or  motors,  which  alternately  charge 
two  sets  of  storage  batteries  of  six  or  seven  cells  each,  through  a 
suitably  designed  switchboard.  This  equipment  is  located  as  con- 
venience dictates,  but  as  a  rule,  the  batteries  are  placed  in  the  lower 


RAILWAY  SIGNALING  23 

floor  of  the  operating  tower.  The  electrical  power  required  by  an 
electro-pneumatic  plant  is  very  small,  the  machine  operating  the 
largest  plant  in  the  world,  St.  Louis  Terminal,  Tower  I,  requiring 
an  average  discharge  of  only  five  to  six  amperes. 

INTERLOCKING    MACHINE 

In  Fig.  6  is  illustrated  the  Boston  Southern  Station 
Machine,  from  which  a  clear  understanding  can  readily  be 
had  of  its  construction  and  method  of  operation.  For  the  guidance 
of  operators,  especially  when  first  learning  the  "combination"  of 
large  interlocking  machines,  it  is  customary  to  equip  such  machines 
with  a  miniature  reproduction  of  the  yard  (known  in  signal  par- 
lance as  a  "Track  Model")  on  which  all  switches  and  signals  are 


FIG.    7 — SMALL    MACHINE    SHOWING    MECHANICAL    LOCKING,    THE 
COMBINATION,    THE    INDICATION    AND    LOCK    MAGNETS 

numbered  to  correspond  with  the  levers  controlling  them  and  all 
tracks  are  designated  by  their  proper  letters,  names  or  numbers. 
The  switches  on  this  model  board  are  connected  mechanically  to 
their  controlling  levers  and  move  in  accordance  with  them,  thus 
permitting  the  operator  to  see  at  a  glance  the  particular  route  or 
routes  he  has  "lined  up."  On  comparatively  small  plants  having 
but  few  routes  a  track  model  is  not  necessary  but  on  large  and  com- 
plicated installations  it  is  of  great  assistance  to  the  operators. 

The  operating  levers  point  alternately  up  and  down,  those 
pointing  upwards  and  having  odd  numbers  being  switch  levers  and 
the  others  signal  levers.  All  machine  levers  are  numbered  from  the 
left.  Switch  levers  stand  normally  at  an  upward  angle  of  30  de- 


24  RAILWAY  SIGNALING 

grees  to  the  left  of  the  vertical,  and  when  operated,  are  moved 
through  an  arc  of  60  degrees.  The  normal  position  of  signal  levers 
is  vertically  downward  from  which  they  can  be  operated  30  degrees 
to  the  right  or  left,  being  capable  of  three  distinct  positions,  the  use 
of  which  will  be  explained  later.  A  system  of  mechanical  locks  is 
provided  between  levers  which  is  identical  in  every  respect,  except 
in  size,  with  that  described  in  a  previous  article  treating  of  the  me- 
chanical interlocking  machine.  To  each  lever  of  the  electro-pneu- 
matic machine  is  secured  a  horizontal  shaft,  which  performs  three 
distinct  functions.  It  drives  the  mechanical  locking  bars  by  means 
of  racks  and  segmental  gears ;  it  rotates  a  hard  rubber  roller  carry- 
ing phosphor  bronze  contact  bands,  thereby  opening  and  closing  the 
various  controlling  and  selecting  circuits  for  switches  and  signals; 
and  lastly,  it  engages  with  the  "indication  latches"  which  are  act- 
uated by  magnets,  the  energizing  of  which  is  effected  by  such 
switches  and  signals.  Each  switch  lever  is  equipped  with  two  such 
magnets,  one  known  as  the  "normal"  and  the  other  as  the  "reverse" 
indication  magnet,  and  each  signal  lever  is  equipped  with  one, 
known  as  the  "lock"  magnet.  The  object  of  these  locks,  or  "indica- 
tions" is  to  insure  that  the  movement  of  each  signal  and  switch 
shall  correspond  with  the  movement  of  the  lever  governing  it.  To 
the  shaft  of  each  lever  a  segment  is  attached  for  every  lock,  which 
engages  with  the  latches  of  such  locks  and  prevents  the  lever  from 
being  moved  from  one  extreme  position  to  the  other  until  the  switch 
or  signal  has  responded  to  the  preliminary  movement  and  through 
circuit  controllers  closed  the  circuit  of  the  "indication"  or  "lock" 
magnet,  thereby  lifting  the  latch  from  the  segment  and  permitting 
the  operator  to  complete  the  stroke  of  the  lever. 

Between  the  mechanical  locking  bed  on  the  machine,  and  the 
bracket  which  carries  the  indication  magnets,  is  a  hard  rubber  plate. 
To  this  plate  by  means  of  screws  are  fastened  phosphor  bronze 
springs.  These  springs  extend  upward  and  bear  against  bronze 
bands  on  the  hard  rubber  roller,  and  when  it  is  desired  to  control  a 
signal  from  one  or  more  switch  levers,  the  springs  are  made  to  bear 
against  the  rollers  of  the  levers,  and  the  bands  on  the  rollers  so  set 
with  relation  to  the  position  of  the  lever  that  the  circuit  may  be 
opened  or  closed  with  the  lever  in  any  position  desired.  These 
springs  form  what  is  generally  known  as  the  "Combination."  Fig. 
7  is  a  top  view  of  a  small  electro-pneumatic  machine,  and  shows  the 
mechanical  locking,  the  combination,  and  the  indication  and  lock 
magnets. 


RAILWAY  SIGNALING  25 

At  the  back  of  each  hard  rubber  roller,  on  switch  levers,  is  a 
short  section  of  hard  rubber  mounted  loosely  so  as  to  allow  the 
switch  lever  to  rotate  50  degrees  of  its  stroke  without  being  effected, 
but  after  the  switch  has  responded  to  the  first  movement  of  its  lever 
and  been  locked  in  its  new  position,  the  segment  released  and  the 
lever  now  free  to  be  put  to  its  extreme  position  by  the  operator,  the 
last  10  degrees  of  its  stroke  acts  on  the  loose  collar  and  closes  two 
pairs  of  contact  springs  which  are  alternately  closed  in  one  position 
and  open  in  the  other.  These  springs  form  part  of  the  controller 


....     *      ii™ 


FIG.     8 — SECTIONAL     VIEW     OF     ELECTRO-PNEUMATIC     INTERLOCKING     MACHINE 

circuit  for  the  indication  magnets.  This  loose  piece  is  held  from 
following  the  roller  in  its  preliminary  movement  or  from  shifting  by 
means  of  a  toggle  joint  under  the  influence  of  a  coil  spring. 

For  the  control  of  switches,  five  bands  are  mounted  on  the 
hard  rubber  roller  (two  of  them  being  on  the  loose  collar).  For 
the  control  of  signals  two  bands  only  are  required.  In  addition  to 
the  regular  bands  on  the  roller,  each  signal  lever  is  provided  with  a 
latch  circuit  controller  which  is  normally  open,  and  which  closes  a 
circuit  on  the  lock  magnet  with  the  first  movement  of  the  latch,  rea- 
sons for  which  will  be  explained  later. 

The  electro-pneumatic  machine  is  enclosed  in  an  oak  or  walnut 


RAILWAY  SIGNALING 


' 


RAILWAY  SIGNALING  27 

case,  the  top  being  covered  with  glass,  enclosed  in  frames,  so  that 
the  mechanical  locking  and  combination  can  easily  be  inspected. 
Sectional  views  of  the  electro-pneumatic  machine  are  shown  in  Figs. 
8  and  9. 

OPERATING   TOWER 

This  tower  is  usually  two  stories  high,  built  of  brick  and  of 
sufficient  size  to  properly  accommodate  the  interlocking  machine, 
provide  space  for  the  operators,  train  director,  telephones,  telegraph 
instruments,  etc.  As  previously  mentioned,  the  machine  is  usually 
installed  on  the  second  floor,  to  enable  the  director  and  operators  to 
get  a  good  view  of  the  tracks  signalled. 

In  the  tower,  in  plain  view  of  the  director  and  operators,  are 
the  annunciators,  usually  in  the  form  of  miniature  signals  enclosed 
in  iron  or  wood  cases,  the  blades  of  which  are  moved  by  rods  con- 
nected directly  to  the  armatures  of  vertical  magnets.  Working  in 
connection  with  these  annunciators,  is  a  bell  arranged  to  ring  as  the 
annunciators  move  from  one  position  to  the  other,  thereby  notifying 
the  operator  of  the  approach  of  a  train  on  the  track  which  the  an- 
nunciator indicates. 

Fouling  point  indicators  are  also  frequently  used  to  indicate  to 
the  operator  when  a  train  has  cleared  the  fouling  point  of  a  partic- 
ular switch  for  his  guidance  in  setting  up  routes  for  other  trains. 
These  annunciators  are  controlled  through  relays  operated  automat- 
ically by  a  section  of  track  extending  back  to  the  fouling  point. 


28 


RAILWAY  SIGNALING 


PNEUMATIC   AND    ELECTRIC    CONNECTIONS 

The  pipes  for  carrying  the  compressed  air  are  of  galvanized 
iron  and  are  tested  under  greater  pressure  than  they  are  ever  called 
upon  to  stand  under  ordinary  working  conditions.  The  main  air 
pipe  is  provided  with  expansion  joints  suitably  placed,  to  take  care 
of  any  expansion  or  contraction  due  to  change  in  temperature. 
Gate  valves  are  also  installed  along  the  line  for  shutting  off  the  air 
at  any  desired  place  in  case  of  a  break  in  the  pipe  without  the  ne- 
cessity of  shutting  down  the  compressors  and  completely  "tying 


H    R.  R         6  <iS   T  A  N  D  A  R  f>\   \      I  0  0  -  U  B.       R 


FIG.     IO — PLAN  AND  ELEVATION   OF    SIMPLE   SWITCH 


up"  the  plant.  The  branch  connections  are  also  provided  with  stop 
cocks  so  that  the  air  can  be  shut  off  at  any  particular  switch  or  sig- 
nal at  any  time  without  interfering  with  any  of  the  others.  The 
pipes  are  usually  encased  in  wooden  conduits  and  placed  under 


RAILWAY  SIGNALING 


29 


ground,  those  crossing  tracks  being  placed  deep  enough  to  prevent 
any  disturbance  by  section  men  when  raising  or  lowering  tracks  or 
tamping  ties. 

The  wires  from  the  machine  for  controlling  the  various  func- 
tions are  usually  carried  in  yellow  pine  conduit  or  "trunking"  to 
protect  them  from  mechanical  injury.  This  conduit  is  usually  sup- 
ported on  oak  stakes  or  foundations  about  six  inches  above  the 
ground,  although  it  is  sometimes  buried  so  as  to  come  level  with  the 
top  of  the  ground.  The  former  method  is  preferable  to  the  latter 


MAGNETS 


FIG.     II — SECTIONAL  VIEW  OF  CYLINDER  AND  VALVE 


being  much  easier  of  access  and  more  apt  to  be  free  from  moisture. 
The  insulated  wires  between  the  machine  and  the  various  functions 
are  usually  made  up  in  five  conductor  cables,  as  five  wires  are  re- 
quired for  the  control  of  each  switch  or  crossover  and  the  signals 
are  usually  so  located  that  a  cable  can  be  used  to  advantage  for  two 
of  them.  The  conductors  of  these  cables  are  made  of  different  col- 
ors so  that  the  five  conductors  can  be  easily  distinguished.  A  per- 
centage of  spare  wires  is  usually  provided  for  use  in  case  of  breaks 
or  grounds.  Terminal  boxes  are  installed  at  frequent  intervals 


30  RAILWAY  SIGNALING 

which  form  convenient  places  for  conducting  tests  and  for  making 
joints,  as  no  splices  are  allowed  in  the  conduits. 


SWITCHES — LOCKS — SIGNALS 

The  switches  are  operated  by  switch  and  lock  movements  act- 
uated from  air  cylinders  of  suitable  size.  Both  the  cylinders  and 
movements  are  rigidly  attached  to  iron  plates  which  in  turn  are 
bolted  to  the  switch  ties  of  the  switch  to  be  operated.  Working  in 
conjunction  with  each  switch  is  a  "detector"  bar,  the  operation  and 
function  of  which  was  described  in  the  chapter  on  mechanical 
interlocking.  P'ig.  10  shows  such  a  movement  and  detector  ap- 
plied to  a  single  switch.  The  switch  and  lock  movement  has  a 
total  stroke  of  eight  inches.  The  first  two  inches  of  its  movement 
unlocks  the  switch  and  throws  the  detector  bar,  the  next  four  inches 


Indication  Ma 


Switch  Valve  Magnets 
Indication  Box 


Indication  Circuit 


Contacts  conn  oil  in  j_ 
switch  valve 
Switch  lever 

Normal  Indicatioji  t» 


Reverse  Indicatiori 


Common  Return 


FIG.    12 — CONNECTIONS  FOR  A  SINGLE  SWITCH  CIRCUIT 

shifts  the  switch  from  one  position  to  the  other  and  the  last  two 
inches  locks  it  in  its  new  position. 

An  electric  switch  valve  which  controls  the  admission  of  air  to, 
or  the  discharge  of  air  from,  the  cylinder  is  attached  to  each  switch 
cylinder.  In  one  of  the  chambers  of  the  switch  valve,  and  con- 
stantly under  pressure  is  a  slide  valve  mounted  in  a  manner  similar 
to  that  of  a  steam  engine.  The  valve  lies  between  the  ends  of  two 
small  plungers  extending  from  the  pistons  of  two  single  acting  cyl- 
inders which  are  each  provided  with  a  separate  magnet  and  pin 
valve  to  control  their  movement.  The  air  for  these  pin  valves  is 
forced  through  a  port  drilled  from  their  chamber  to  that  of  the  slide 
valve.  In  practice  one  or  the  other  of  the  pin  valve  magnets  is 
energized  by  current  from  the  tower  at  all  times.  Consequently 
the  pressure  is  always  against  one  or  the  other  of  the  pistons  used 


RAILWAY  SIGNALING  31 

for  shifting  the  slide  valve.  A  pneumatic  bolt  lock  is  applied  to  the 
slide  valve  and  it  is  absolutely  necessary  that  this  be  withdrawn  be- 
fore the  valve  can  be  operated.  This  bolt  lock  consists  of  a  bal- 
anced piston  the  plunger  of  which  is  normally  forced  into  a  recess 
in  the  slide  valve  by  the  action  of  a  coil  spring.  The  air  pressure  is 
normally  confined  to  the  cylinder  both  above  and  below  the  piston, 
the  former  by  a  pin  valve  controlled  by  an  electro-magnet.  When 
the  magnet  is  energized,  the  air  is  exhausted  from  above  the  piston 
and  the  pressure  below  it  raises  it,  compresses  the  coil  spring  and 
lifts  the  bolt  lock  from  the  slide  valve.  When  the  magnet  is  again 
de-energized  further  escape  of  air  from  above  the  piston  is  prevent- 
ed and  the  coil  spring  again  forces  the  bolt  lock  into  the  slide  valve. 
A  sectional  view  of  a  cylinder  and  valve  is  shown  in  Fig.  n.  Cylin- 


FIG.     13 — CONNECTIONS  FOR  CROSS-OVER  CIRCUIT 

ders  for  the  operation  of  single  switches  are  usually  five  or  six 
inches  in  diameter,  and  for  the  operation  of  slip  switches  and  mov- 
able point  frogs,  seven  and  one-half  inches.  One  end  of  a  double 
slip  and  the  movable  frog  are  generally  operated  from  the  same  cyl- 
inder, the  cylinder  being  placed  at  the  frog  points,  working  them 
through  two  switch  and  lock  movements  coupled  in  tandem,  and  by 
mechanical  connections  working  the  slip  points  through  a  single 
switch  and  lock  movement  at  the  slip  end.  When  hooked  up  in  this 
manner,  the  switch  indication  box  is  placed  on  the  movement  far- 
thest away  from  the  cylinder. 

In  addition  to  the  five  wires  mentioned  previously  as  being  re- 
quired for  the  control  of  a  switch,  there  is  a  common  return  wire 
for  the  entire  interlocking.  The  wires  are  known  by  the  function 
they  control,  viz. — a  normal,  a  reverse  and  a  lock  control ;  a  normal 
and  a  reverse  indication.  The  circuits  for  a  single  switch  are  shown 
in  Fig.  12.  By  referring  to  this  diagram  it  may  be  seen  that  the  first 


RAILWAY  SIGNALING 


movement  of  the  lever  in  the  machine  energizes  the  centre  or  "lock" 
magnet  on  the  switch  valve  before  the  circuit  is  broken  on  the  re- 
verse magnet,  and  by  so  doing  withdraws  the  bolt  lock  from  the 
slide  valve.  Continuing  this  movement  energizes  the  reverse  shifting 
magnet,  and  by  unseating  a  pin  valve  admits  the  air  to  the  reverse 
auxiliary  cylinder,  at  the  same  time  de-energizing  the  normal  mag- 
net and  releasing  the  aiir  in  the  normal  auxiliary  cylinder,  thereby 
moving  the  slide  valve  to  the  opposite  side  by  means  of  the  piston 


Roller 


Connectors  or  Terminal 
B|>ard  in  Interlocking  MachineAj! 

ng  Arranged  on  Combination 
to  Open  Normal  at    vetr 
stirt  of  lever  stroke  and  close    ^ 
re  rersed  at  very  end  of  stroke 


FIG.     14 — CONNECTIONS  FOR  A   SINGLE  SWITCH,  USING  TRACK  CIR- 
CUIT   IN    LIEU    OF    DETECTOR   BAR 

and  piston  rod.  The  shifting  of  the  slide  valve  in  turn  transfers 
the  air  pressure  from  one  end  of  the  cylinder  to  the  other  and  throws 
the  switch,  through  the  medium  of  the  switch  and  lock  movement. 
When  a  switch  is  normal,  as  shown  at  Fig.  12,  the  first  move- 
ment of  the  lever  to  the  reverse  position  breaks  the  normal  indication 
magnet  control  on  the  machine  and  drops  the  armature  and  latch. 
The  last  movement  of  the  switch  closes  the  reverse  indication  con- 
trol circuit  through  the  indication  box  contact  springs,  showing  that 


RAILWAY  SIGNALING 


33 


the  switch  has  been  shifted  and  locked  in  its  new  position,  lifts  the 
armature  and  latch,  and  releases  the  segment  which  allows  the  lever 
to  be  placed  in  the  extreme  reverse  position  and  the  latch  dropped. 
The  placing  of  the  lever  in  the  extreme  reverse  position  also  releases 
any  mechanical  locking  that  may  depend  on  that  particular  lever. 
The  moving  of  a  switch  in  the  opposite  direction  reverses  the  order 
of  these  operations.  When  two  or  more  switches  are  operated  from 
one  lever  by  two  independent  cylinders —  as  for  example  a  crossover 
— the  indication  circuit  is  carried  through  indication  boxes  on  each 
movement  in  series  as  shown  in  Fig.  13. 

From  the  above  description,  it  is  apparent  that  the  objections 
offered  to  the  use  of  switch  and  lock  movements  in  mechanical 
work,  viz: — the  small  stroke  available  for  locking  the  switch,  the 
danger  of  forcing  the  lever  completely  over 
through  lost  motion  in  the  connections,  and 
that  a  switch  may  not  correspond  to  the  posi- 
tion of  its  lever  due  to  broken  connections, 
do  not  hold  good  in  the  electro-pneumatic  in- 
terlocking system,  as  a  positive  indication 
must  be  received  in  the  tower  that  the  switch 
has  make  its  complete  stroke  and  has  been 
locked,  before  its  lever  can  be  put  to  the  full 
normal  or  reverse  position. 

In  many  cases  "electric  detector"  circuits 
are  installed  in  lieu  of  the  mechanical  de- 
tector bars,  in  which  case,  a  short  section  of 
track  is  insulated  ahead  of  the  switch,  and 
the  indication  wire  passed  through  a  relay 
contact,  the  relay  being  actuated  by  a  battery 
connected  to  the  rails  of  the  track.  Where 
"detector  circuits"  are  used  the  switch  lever  is  equipped  with  a  latch 
circuit  controller  similar  to  the  one  applied  to  signal  levers,  which 
closes  a  circuit  on  the  indication  magnet  through  the  relay  contact. 
This  is  illustrated  in  Fig.  14.  From  a  reference  to  this  figure  it  is  ob- 
vious that  both  the  normal  and  reverse  indication  magnets  are  nor- 
mally on  open  circuit,  and  either  one  is  energized  by  the  first  move- 
ment of  the  lever  latch  providing  the  "track  section"  is  unoccupied. 
High  signals  are  of  iron  pipe  construction.  The  spectacle  cast- 
ing carrying  the  semaphore  arm  and  the  colored  glass  for  night  indi- 
cation are  so  counterweighed  as  to  always  gravitate  to  the  "danger" 
or  "stop"  position.  Hence  it  is  only  necessary  to  use  a  single  stroke 


FIG.  15 — SIGNAL  MOVE- 
MENT AND  CIRCUIT 
BREAKER 


34 


RAILWAY  SIGNALING 


cylinder  to  work  against  gravity  for  the  operation  of  signals,  and  in- 
dicate to  the  operator  in  the  tower,  that  the  signal  is  in  the  "stop" 
position. 

Signal  cylinders  are  ordinarily  three  inches  in  diameter,  and  are 
fitted  with  an  electro-magnet  and  valve  for  the  controlling  of  the 
admission  and  discharge  of  air.  At  the  side  of  each  cylinder  is 
clamped  a  circuit  breaker  so  arranged  that  the  circuit  is  made  only 
when  the  signal  is  at  "danger."  A  signal  movement  and  circuit 
breaker  are  shown  in  Fig.  15. 

As  previously  stated,  each  signal  lever  in  the  machine  is  equip- 
ped with  a  latch  circuit  controller,  the  object  of  which  is  to  close  a 
contact  as  soon  as  the  latch  is  raised,  thereby  completing  a  circuit 


Circuit  Closer 


FIG.    l6 — DIAGRAM    OF  SIGNAL  CIRCUITS 

through  the  circuit  controller  on  the  signal  cylinder  and  the  lock 
magnet  on  the  machine,  and  by  so  doing  lift  the  armature  and  latch, 
release  the  segment  and  allow  the  lever  to  be  moved  to  the  right  or 
left,  depending  on  the  mechanical  locking  and  signal  to  be  operated. 
The  movement  of  the  lever  closes  the  circuit  controlling  the  magnet 
on  the  signal  cylinder  through  one  of  the  bronze  bands  on  the  roller. 
The  magnet  in  turn  opens  the  valve  and  allows  the  air  to  enter  the 
cylinder  and  clear  the  signal.  A  diagram  of  signal  circuits  is  shown 
in  Fig.  1 6.  This  diagram  shows  that  when  more  than  one  signal  is 
controlled  from  the  same  lever  the  lock  wire  is  carried  through  cir- 
cuit breakers  on  each  of  the  signals  so  that  it  is  absolutely  necessary 
for  all  of  them  to  be  at  "danger"  before  the  lock  magnet  can  be 
energized  and  the  lever  restored  to  its  normal  position. 

Low  or  dwarf  signals — used  between  tracks — are  operated  by 
means  of  direct  acting  cylinders,  which  act  against  strong  coil 
springs  so  arranged  as  to  be  compressed  when  air  is  applied  to  the 
cylinders,  in  clearing  the  signals  and  to  force  the  signals  back  to 


RAILWAY  SIGNALING 


35 


''danger"  when  the  air  pressure  is  removed.  Dwarf  cylinders  differ 
from  those  of  high  signals  in  that  they  are  movable  and  their  pistons 
are  stationary.  Their  piston  rods  are  hollow  and  serve  as  ports  for 
the  admission  and  discharge  of  air  to  and  from  the  cylinder.  The 
cylinder  is  directly  connected  to  the  semaphore  shaft  by  means  of  a 
rod  enclosed  in  the  post.  Fig.  17  shows  a  sectional  view  of  a  dwarf 
signal.  At  the  side  of  each  dwarf  signal  cylinder  but  insulated 
therefrom  is  a  brass  plate  which  closes  a  circuit  when  the  signal  is 
in  the  stop  position  by  resting  against  contact  springs  fastened  to 


AIR  DUCT 

ELEVATION  SECTIONAL    VIEW 

FIG.    17 —  DWARF   SEMAPHORE   SIGNAL 


the  base  of  the  signal.  This  circuit  controller  performs  the  same 
functions  as  the  one  previously  described  in  connection  with  the 
high  signal. 

In  mechanical  work,  it  is  not  considered  good  or  safe  practice 
to  operate  more  than  one  signal  from  one  lever  although  two  or 
more  can  be  so  operated  through  what  is  known  as  a  "selector."  It 
is  sufficient  here  to  say  that  selectors  in  mechanical  work  are  very 
unsatisfactory  and  unreliable.  In  electro-pneumatic  interlocking 


RAILWAY  SIGNALING 


this  selection  is  done  electrically  in  the  tower 
through  the  "combination"  on  the  hard  rubber 
roller  of  the  machine  levers.  Opposing  signals 
for  the  same  track,  or  signals  that  govern  traffic 
up  to  the  same  track  from  converging  tracks, 
may  be  worked  with  perfect  safety  from  the  same 
lever  in  the  electro-pneumatic  interlocking  sys- 
tem. As  a  means  of  illustrating  how  this  select- 
ing is  accomplished,  the  layout  shown  in  Fig.  18 
is  assumed.  Previous  mention  was  made  that 
the  normal  position  of  signal  levers  is  in  the  cen- 
tral position  and  that  they  are  capable  of  being- 
moved  to  the  right  or  left.  By  reference  to  Fig. 
1 6  it  may  be  seen  how  opposing  signals  for  the 
same  track  are  operated  from  a  right  or  left 
hand  movement  of  the  lever.  By  referring  to 
Fig.  1 8  it  may  be  seen  that  but  one  train  can 
move  out  of  the  yard  to  the  main  track  at  any 
one  time  and  the  signals  governing  movements 
to  the  main  track  are  all  operated  from  the  same 
lever,  shown  as  No.  4.  Here  is  where  the  "com- 
bination" on  the  electro-pneumatic  machine  is 
used  to  advantage  for,  by  it,  current  is  supplied 
to  the  desired  signal.  The  "combination"  for 
the  above  layout  is  shown  in  Fig.  19.  If,  for  ex- 
ample, it  is  desired  to  clear  the  signal  on  track 
5,  it  is  first  necessary  to  reverse  switches  5  and 
ii,  so  that  the  track  will  be  in  shape  for  the  train 
to  proceed  over  it.  Signal  lever  4  is  then  moved 
to  the  left,  which  will  energize  magnet  on  signal 
4Le,  through  closed  circuit  breakers  on  levers  5, 
/,  p,  and  11.  A  study  of  the  layout  and  combina- 
tion will  show  that  any  one  of  the  signals  can 
be  given  through  the  contacts  on  the  rollers  of 
the  switch  levers. 


AUXILIARY  APPLIANCES 


The  control  of  annunciators  is  accomplished 
by  means  of  a  section  of  bonded  and  insulated 
track  at  the  distance  from  the  tower  at  which  it  is 
desired  to  announce  an  approaching  train.  At  one 


RAILWAY  SIGNALING 


37 


end  of  this  insulated  section  is  located  the  battery  and  at  the  other  a 
relay.  The  annunciator  magnet  control  is  carried  through  a  con- 
tact on  this  relay.  As  soon  as  a  train  strikes  this  bonded  section  the 
relay  is  shunted.  This  in  turn  opens  the  annunciator  control  and 
causes  the  miniature  signal  to  assume  the  "danger  position"  and  the 


J3 


•tn 


4Ll 


14 


f 


1.1 


*% 


4L 


1L: 


rt 


*i 


2L 


Battery 


FIG.  19 — "COMBINATION"  FOR  TRACK  LAYOUT  SHOWN  IN  FIG.  13 

annunciator  in  so  moving  closes  a  circuit  on  a  single  stroke  bell, 
thus  indicating  to  the  towerman  that  a  train  is  approaching. 

Track  sections  are  also  installed  for  automatically  setting  sig- 
nals to  the  "danger"  or  "stop"  position,  after  a  train  has  passed 
them  and  preventing  them  from  again  being  cleared  as  long  as  the 
train  is  on  the  track  section,  but  this  feature  will  be  dealt  with  in  a 
later  article. 


CHAPTER  III 

ELECTRIC  INTERLOCKING 

A  VERY  long  stride  in  the  direction  of  improved  interlocking 
apparatus  was  made  when  electricity  came  into  use  as  the 
motive  power  for  operating  the  switches  and  signals. 
That  the  use  of  electricity  for  the  purpose  supplied  a  want,  is  proved 
by  the  rapidity  with  which  electric  interlocking  has  assumed  a  place 
second  to  none  in  the  estimation  of  the  railroad  world.  Electric 
interlocking  was  first  introduced  commercially  in  1900.  Since  that 
time  growth  in  the  number  of  installations  has  been  very  rapid ;  the 
number  increasing  in  a  ratio  such  that  the  number  of  installations  in 
any  year  exceeds  that  of  tjie  two  preceding  years  combined. 

The  superiority  of  electricity  as  a  motive  power  in  interlocking 
work,  as  well  as  for  a  great  many  other  purposes,  is  due  to  the 
facility  with  which  it  can  be  stored  and  retained  for  indefinite  pe- 
riods of  time  with  very  small  loss  from  leakage,  and  to  the  small 
loss  incurred  in  transporting  it  from  the  point  where  it  is  generated 
or  stored,  to  the  point  where  it  is  to  be  used.  The  conversion  of 
electrical  into  mechanical  energy  can  be  effected  with  a  high  degree 
of  efficiency  the  question  of  efficiency  of  conversion,  being,  how- 
ever, of  less  importance  in  interlocking  work  than  the  high  degree 
of  insulation  that  is  possible  to  attain.  The  circuits  of  an  inter- 
locking plant  can  easily  be  so  well  insulated  that  the  loss  on  account 
of  leakage  is  practically  nothing,  and  faults  in  insulation  can  very 
easily  be  detected  and  removed;  in  fact,  immediate  attention  is 
called  to  faults  of  a  serious  nature  in  electric  circuits,  by  their  in- 
terference with  the  proper  operation  of  the  plant. 

When  a  switch  lever  in  a  mechanical  interlocking  plant  is 
moved  from  normal  to  reverse  and  latched,  the  locking  between  it 
and  the  signal  lever,  controlling  the  signal  governing  movements 
over  the  switch  reversed,  is  immediately  released.  When  the  lever 
is  reversed  and  latched,  it  is  assumed  that  the  switch  has  followed 
the  movement  of  the  lever  and  is  also  reversed  and  locked.  The 
possibility  of  the  pipe  line  breaking,  or  buckling  enough  to  allow 
the  lever  to  be  put  into  full  reversed  position  with  the  switch  only 
partly  reversed,  is  not  considered.  But  when  electric  power  is  used 


RAILWAY  SIGNALING 


39 


for  operating  the  switches  (and  the  same  may  be  said  of  other 
forms  of  power),  the  movement  of  the  lever  merely  turns  on  the 
power  and  it  is  not  safe  to  assume  that  the  switch  necessarily  fol- 
lows the  movement  of  the  lever  and  takes  up  a  position  correspond- 
ing. The  circuit  may  be  open  at  any  one  of  a  number  of  places 
so  that  current  will  not  reach  the  motor  at  all;  or  the  movement 
of  the  switch  may  be  obstructed  so  that  the  motor  is  unable  to 
move  it.  In  order  that  a  failure  of  the  switch  to  respond  to  the 
movement  of  its  controlling  lever,  may  not  result  in  dangerous 
consequences,  the  lever  movement  is  divided  into  two  parts : 
the  preliminary  movement  for  closing  the  operating  circuit  of  the 
motor  and  the  final  movement  for  releasing  the  locking  of  other 
levers.  The  lever  is  stopped  at  the  end  of  the  preliminary  move- 
ment by  a  latch  known  as  the  indication  latch,  because  its  disen- 
gagement from  the  lever  serves  as  an  indication  that  the  switch 


R                                     P       ' 

n 

P 

BI= 

FIG.  20 

has  been  moved  home  and  locked.  The  latch  is  lifted  and  the  lever 
freed  to  make  its  final  movement  at  the  proper  time  by  an  electro- 
magnet or  motor  known  as  the  indication  magnet  or  the  indication 
motor. 

The  necessity  for  an  indication  or  automatic  release  of  the 
locking  when  power  of  any  kind  is  used  for  operating  switches, 
was  recognized  from  the  first,  but  the  problem  still  confronting  the 
signal  engineer  was  to  find  a  suitable  source  of  current  for  energiz- 
ing the  indication  magnet.  The  first  thought  that  would  occur 
to  one  trying  to  solve  the  problem,  would  be  to  employ  the  main 
source  of  current  used  in  operating  the  plant,  for  energizing  the 
indication  magnet,  and  have  the  switch  mechanism  operate  a  cir- 
cuit controller  to  close  the  indication  circuit  at  the  proper  time. 
Such  a  method  is  shown  diagrammatically  in  Fig.  20,  divested  of  most 
of  the  apparatus  and  circuit  controllers  not  directly  concerned  in 
the  formation  of  the  indication  circuits.  An  indication  circuit  is 


40  RAILWAY  SIGNALING 

closed  in  either  extreme  position  of  the  track  switch,  by  the  circuit 
closer  C  actuated  by  the  rod  H  which  is  connected  to  some  point  of 
the  switch  movement,  preferably  to  the  lock  bar.  .  It  can  easily  be 
seen  by  a  mere  inspection  of  the  diagram,  that  an  accidental  contact 
of  the  wire  Q  with  the  common  return  wire,  such  as  could  easily 
happen  through  faulty  insulation,  and  as  indicated  by  the  dotted 
line  X,  would  cause  an  indication  to  be  given  irrespective  of  the 
position  of  the  controller  C  and,  therefore,  irrespective  of  the  posi- 
tion of  the  track  switch.  An  actual  contact  of  the  two  wires  is  not 
required  to  produce  this  result.  If  both  are  grounded  the  effect  is 
the  same.  No  matter  how  good  the  insulation  may  be  or  how  care- 
fully the  work  of  construction  and  installation  may  be  done,  there  is 
always  the  possibility  that  the  insulation  may  break  down.  An 
indication  given  by  a  current  drawn  from  the  main  source  of  supply 


FIG.   21 

which  operates  the  plant,  is,  therefore,  little  better  than  no  indica- 
tion at  all.  It  will  be  noticed  that  this  method  of  operation  and 
indication  requires  four  wires,  two  operating  and  two  indication, 
extending  between  the  lever  and  the  switch,  in  addition  to  a  wire 
which  is  common  to  all  switches  lying  in  the  same  general  direction 
from  the  cabin. 


DEVELOPMENT  OF  ELECTRIC   INTERLOCKING 

The  first  real  step  towards  developing  a  practical  system  of 
electric  interlocking,  was  made  when  a  means  was  discovered  for 
utilizing  a  current  generated  by  the  switch  operating  motor  itself, 
for  actuating  the  indication  magnet.  This  method  is  illustrated 
by  Fig.  21  in  which  the  parts  are  shown  in  the  proper  connection 
for  generating  the  indication  current.  During  the  switch  movement 
supposed  to  be  just  completed,  the  controller  CC'  was  in  the  upper 
position  when  current  flowed  through  the  armature  and  fields  in  the 
direction  of  the  arrow  j,  and  the  counter  electro-motive  force  had 


RAILWAY  SIGNALING  41 

the  direction  indicated  by  the  arrow  2.  At  the  instant  the  switch 
movement  is  completed,  the  controller  CC  is  shifted  to  the  position 
shown,  which  puts  the  motor  and  indication  magnet  on  a  circuit 
independent  of  the  battery.  The  electro-motive  force  induced  in  the 
armature,  which  is  still  rotating  due  to  the  momentum  previously 
acquired,  drives  a  current,  through  the  indication  magnet  in  the  di- 
rection of  arrows  2.  It  is  obvious  that  the  only  effect  that  a  con- 
nection between  the  wire  R  and  the  common  wire  could  have,  would 
be  to  prevent  current  reaching  the  indication  magnet ;  thus  the 
error,  if  any,  would  be  on  the  side  of  safety.  If  the  wire  R  should 
by  accident  become  connected  to  N,  current  would  flow  through  the 
indication  magnet,  but  harm  from  this  is  prevented  by  putting  an- 
other magnet  with  its  coils  in  circuit  with  the  wire  N,  directly  un- 
der the  indication  magnet,  so  that  the  indication  armature  rests  nor- 
mally on  its  poles.  So  long  then  as  current  is  flowing  in  the  wire  N, 
the  indication  magnet  will  be  unable  to  lift  the  armature,  no  matter 
how  strongly  it  may  be  energized.  If  the  wire  N  should  be  broken 
and  another  live  wire  should  at  the  same  time  become  connected 
with  the  wire  R,  a  false  indication  might  result ;  but  this  requires 
the  simultaneous  happening  of  two  things,  either  of  which  alone 
would  be  immediately  discovered  and  removed.  Interlocking  ap- 
paratus is  considered  safe  when  its  wrong  operation  requires  such 
a  coincidence. 

The  apparatus  shown  at  5  is  employed  for  removing  the  only 
remaining  chance  for  false  indication,  not  taken  care  of  by  the  means 
previously  mentioned.  It  comprises  two  magnets,  one  in  each  ope- 
rating circuit,  acting  on  a  contact  lever  capable  of  bearing  on  a 
fixed  contact  on  either  side.  The  lever  and  contacts  form  a  circuit 
switch,  the  function  of  which  is  to  close  the  proper  indication  cir- 
cuit. If  the  operating  circuit  is  good  so  that  current  flows  in  it, 
the  corresponding  indication  circuit  will  be  closed,  but  then  current 
will  flow  in  the  safety  magnet  under  the  indication  magnet  and  will 
prevent  a  premature  indication.  If  the  operating  circuit  happens 
to  be  open,  the  corresponding  indication  circuit  will  not  be  closed, 
so  that  it  will  be  impossible  for  a  stray  current  to  reach  the  indica- 
tion magnet. 

It  will  be  noticed  that  in  Fig.  21  only  two  wires,  besides  the 
common  wire,  are  required  for  the  operation  and  indication  of  the 
switch :  the  operating  wire  for  one  movement  becomes  the  indica- 
tion wire  for  the  next  movement.  This  system,  therefore,  is  not 
only  much  safer  than  that  using  the  main  battery  for  indications,  but 
requires  only  a  little  more  than  half  as  much  wire. 


42 


RAILWAY  SIGNALING 


Fig.  22  shows  an  entirely  different  method  of  obtaining  a  safe 
and  reliable  indication  of  the  movements  of  the  switch.  In  this  the 
indication  current  is  drawn  directly  from  the  main  battery,  but 
it  is  transformed  into  an  alternating  current,  and  an  alternating- 
current  induction  motor  is  employed  for  actuating  the  indication 
latch.  The  transformation  of  the  battery  current  into  an  alternating 
current  is  effected  by  means  of  a  transformer  and  an  apparatus 
for  varying  the  strength  of  the  current  in  its  primary  coil.  The 
transformer  is  located  in  the  cabin  and  its  primary  coil  is  included 
in  the  operating  circuit.  The  secondary  coil  is  connected  directly 
to  a  small  induction  motor  provided  with  suitable  gearing  to  cause 
the  rotation  of  the  armature  to  lift  the  indication  latch.  The  appa- 
ratus for  producing  the  variations  in  the  current  should  be  located 
at  the  switch,  so  that  the  circuit  closer  actuated  by  the  switch  mech- 
anism for  closing  the  indication  circuit  may  be  between  this  appa- 


FIG.  22 


ratus  and  the  transformer.  A  convenient  means  for  producing  the 
variations  in  the  current  is  afforded  by  a  collector  ring  on  the  arma- 
ture shaft  of  the  switch  operating  motor,  connected  to  one  segment 
of  the  commutator.  At  the  end  of  the  switch  movement,  after  it 
has  been  locked,  and  after  the  motor  has  been  disengaged  from  the 
mechanism  by  the  clutch  interposed  between  the  motor  and  the 
mechanism  for  the  purpose,  the  operating  wire  is  switched  from 
the  operating  brush  to  the  brush  bearing  on  the  collector  ring.  The 
motor  armature  will  continue  to  rotate,  driven  by  the  current  enter- 
ing by  way  of  the  collector  ring  and  passing  out  by  way  of  the 
brush  connected  to  the  common  wire,  and  as  the  segment  to  which 
the  ring  is  connected  alternately  approaches  and  then  recedes  from 
the  common  brush,  the  current  in  the  circuit  including  the  primary 
coil  of  the  transformer  will  rise  and  fall  alternately.  The  undulatory 
current  thus  produced,  induces  magnetism  of  a  like  character  in  the 
iron  core,  which  in  turn  generates  an  alternating  current  in  the  sec- 
ondary coil.  The  current  from  the  secondary  flows  through  the 


RAILWAY  SIGNALING  43 

coils  of  the  induction  motor  causing  a  rapid  rotation  of  the  armature 
which  results  in  lifting  the  indication  latch. 

It  can  easily  be  seen  that  a  connection  either  accidental  or  in- 
tentional of  the  wire  N  with  any  other  wire,  would  cause  only  a 
direct  current  to  flow  through  the  primary  coil  of  the  transformer, 
which  would  have  no  effect  on  the  secondary  except  to  produce  a 
single  impulse  at  starting  of  the  current  and  again  at  stopping.  Such 
impulses  have  only  a  barely  perceptible  effect  on  the  armature  of  the 
induction  motor,  and  no  effect,  whatever,  on  the  "centrifuge"  by 
means  of  which  the  rotation  of  the  armature  is  converted  into  a  di- 
rect axial  thrust.  As  the  induction  motor  is  built  to  require  approxi- 
mately one  hundred  alternations  per  second  to  make  it  operative, 
it  is  quite  apparent  that  it  could  not  be  affected  by  any  succession  of 
impulses  that  could  be  produced  by  accident.  The  accidental  con- 
tact of  the  wire  N  with  the  wire  to  another  switch  which  is  in 
the  act  of  indicating,  could  not  result  in  a  false  indication,  because 
it  is  in  connection  with  the  operating  brush  of  the  motor  until  the 
movement  is  completed,  which  would  hold  it  at  a  uniform  potential 
either  high  or  low  and  would  prevent  fluctuation. 

It  will  be  noticed  that  this  system,  also,  requires  only  two  wires 
between  the  operating  lever  and  the  switch ;  the  operating  wire  for 
any  movement  becoming  the  indication  wire  for  the  same  movement. 
During  the  entire  movement  in  either  direction  except  a  small  part  at 
the  end  of  the  movement,  the  two  wires  lead  to  the  operating  brush 
of  the  motor.  Two  field  coils  F  and  F'  are  provided,  one  in  each 
operating  wire,  for  the  purpose  of  reversing  the  direction  of  the 
movement  at  any  point.  The  field  coils  are  so  connected  that  cur- 
rents through  them  from  the  battery  produce  opposite  magnetizing 
effects,  while  the  current  always  flows  in  the  same  direction  through 
the  armature.  A  simple  means  is  thus  afforded  for  reversing  the 
direction  of  rotation  of  the  motor  armature,  which  is  effected  by 
merely  changing  the  position  of  the  operating  lever  and  thus  con- 
necting one  or  the  other  operating  wire  to  battery.  The  quality  of 
reversibilty  is  of  considerable  importance,  for  it  sometimes  happens 
that  the  movement  of  the  switch  points  is  obstructed  by  something 
that  prevents  the  point  coming  up  solidly  against  the  stock  rail.  If, 
in  such  an  event,  the  switch  can  be  put  back  to  its  original  position, 
other  routes  will  be  freed  that  would  be  locked  up  if  the  lever 
had  to  remain  in  its  intermediate  position  until  the  obstruction  is 
removed.  Again,  the  obstruction  may  be  of  such  a  nature  that  it 
may  be  crushed  and  might  fall  out  of  the  way  if  the  pressure  of 


44 


RAILWAY  SIGNALING 


the  point  were  removed.     A  second  attempt  would  then  secure  the 
desired  movement. 

Two  field  coils  cannot  be  used  for  reversing  the  motor  with 
the  system  shown  in  Fig.  21,  because,  as  will  be  seen  later,  such 
means  for  reversal  would  interfere  with  the  proper  performance 
of  the  functions  of  another  essential  piece  of  apparatus.  Reversibil- 
ity is  secured  by  attaching  the  cores  of  two  solenoids  to  the  rod 
connecting  the  blades  of  the  controller  CC'.  By  means  of  these 
solenoids,  one  of  which  is  in  each  operating  circuit,  the  controller 
CC  may  be  manipulated  from  the  cabin. 

SWITCH    OPERATION    BY    STRAY    CURRENTS 

There  is  one  other  consideration  quite  as  important  as  the  in- 
dication, which  must  receive  due  consideration  in  the  design  of  an 
electric  interlocking  system,  and  that  is,  the  provision  of  means  for 
preventing  a  stray  current  reaching  a  switch  or  signal  motor,  and 

M 


FIG.  23 

causing  an  improper  movement  of  the  switch,  or  a  clear  indication 
by  the  signal  when  the  track  ahead  may  not  be  in  proper  condition 
for  a  train  to  pass.  An  improper  movement  of  a  switch,  due  to  a 
stray  current  reaching  it  through  faulty  insulation,  would  have 
practically  the  same  result  as  a  false  indication,  as  it  would  put 
the  switch  in  a  position  not  corresponding  with  the  position  of  the 
lever;  but,  if  there  is  any  difference,  the  condition  would  be  more 
dangerous,  as  there  would  not  be  as  much  likelihood  of  its  being 
discovered  by  the  operator. 

Fig.  23  shows  a  very  effective  means  for  guarding  against  im- 
proper movements  of  switches  and  signals  by  stray  current,  as  ap- 
plied to  the  system  illustrated  in  Fig.  21.  This  means  comprises  a 
circuit  breaker  held  normally  closed  by  current  in  the  coils  of  an 
electro-magnet.  The  electro-magnet  has  two  coils,  one  a  high  resist- 
ance coil  Q  continuously  in  circuit  with  the  main  battery,  and  the 
other  a  low  resistance  coil  in  the  common  lead  of  the  indication 
circuits.  If  current  flows  in  the  coil  P  in  a  direction  to  make  its 


RAILWAY  SIGNALING 


45 


influence  additive  to  that  of  Q,  no  effect  is  produced ;  but  if  it  flows 
in  the  opposite  direction,  the  magnet  will  be  neutralized  and  the 
circuit  breaker  T,  released,  thus  opening  the  main  lead  from  the 
battery  and  cutting  off  current  from  the  entire  plant.  Each  indi- 
cation current  passes  through  the  coil  P,  but  in  the  direction  of  the 
arrow  2,  in  which  direction  it  aids  the  coil  Q  in  holding  the  circuit 
breaker  T;  but  a  current  from  a  live  wire  in  contact  with  the  wire 
R  or  any  of  its  connections  would  flow  back  through  the  coil  P 
in  the  direction  of  the  arrow  I  and  would  cause  the  circuit  breaker 
T  to  open  the  circuit.  It  can  now  be  seen  why  two  field  coils  can- 
not be  used  for  reversing  the  switch  operating  motor,  for  the  use 
of  such  coils  for  the  purpose  would  cause  the  indication  current  to 
flow  in  the  direction  of  the  arrow  /,  and  would  open  the  circuit 
breaker  T  at  each  movement  of  a  switch.  It  can  easily  be  seen 


N 


FIG  24 

that  the  effectiveness  of  the  device  as  a  protection  depends  on  the 
wire  R  being  unbroken  from  the  point  of  improper  contact,  back 
through  the  coil  P,  to  common.  But  this  wire  was  used  as  indi- 
cation wire  in  making  the  last  movement  and  if  it  had  been  broken 
then  the  break  would  have  been  discovered  and  repaired.  A  failure, 
therefore,  requires,  practically,  the  simultaneous  happening  of  two 
things  either  of  which  alone  would  be  discovered  and  repaired  on 
the  first  attempt  to  operate  the  switch.  All  apparatus  used  in  con- 
nection with  the  operation  and  indication  of  the  switch  and  not 
directly  concerned  in  the  operation  of  the  safety  device,  has  been 
omitted  from  the  diagram. 

Another  form  of  safety  device  adapted  especially  to  the  system 
shown  in  Fig.  22,  is  illustrated  in  Fig.  24.  This  apparatus  is  located 
near  the  switch  motor  and  comprises  two  solenoids  for  operating 
circuit  controllers.  Only  enough  of  the  circuits  are  shown  to  illus- 
trace  the  principles  of  its  action  in  preventing  improper  movements. 


46  RAILWAY  SIGNALING 

The  ii.-strument  also  serves  to  open  the  circuit  and  stop  the  current 
when  the  lever  movement  is  completed,  and  to  switch  the  indication 
wire  from  the  brush  bearing  on  the  collector  ring,  to  the  operating 
brush  preparatory  to  the  next  movement.  The  wire  R  is  the  one 
that  will  be  used  to  lead  current  to  the  motor  for  effecting  the  next 
movement  of  the  switch.  The  preliminary  circuit  includes  the  field 
F',  magnet  M',  lever  L ' ,  and  resistance  G' .  Current  in  this  circuit 
will  energize  the  magnet  A/',  causing  it  to  attract  the  lever  L  which 
it  will  pull  up  against  the  contact  K.  If  the  current  is  properly 
started  by  a  movement  of  the  controlling  lever  in  the  cabin,  the 
lever  L'  will  also  be  drawn  back  against  the  contact  J ' ,  thus  cutting 
the  resistance  G'  out  of  the  motor  circuit ;  but  if  the  current  enters 
the  wire  R  through  faulty  insulation  the  lever  in  the  cabin  not  hav- 
ing been  moved,  a  current  will  flow  in  the  circuit  including  the  field 
F,  magnet  M,  lever  L,  and  the  armature,  and  will  result  in  holding 
the  lever  L'  away  from  the  contact  /.  The  latter  circuit  has  no 
extra  resistance  in  it,  while  the  former  includes  the  resistance  G. 
The  current  through  the  field  F  will,  therefore,  be  very  much 
stronger  than  that  through  F',  and  it  will  determine  the  polarity 
of  the  field  magnet,  which  will  be  the  same  as  it  was  in  making  the 
last  movement.  The  motor  armature  will,  therefore,  rotate  idly  in 
the  direction  it  did  in  making  the  last  movement,  and  without  any 
effect  on  the  switch  mechanism.  It  may  be  well  to  mention  here 
that  the  motor  armature  is  connected  to  the  mechanism  by  means 
of  a  clutch  which  permits  the  motor  to  be  disengaged  at  the  end 
of  each  movement,  and  to  run  without  load  while  transforming  the 
current  for  indication.  It  also  runs  without  load  when  the  safety 
device  becomes  operative  to  prevent  an  improper  movement.  The 
counter  electro-motive  force  of  the  motor  acts  as  a  resistance  to  limit 
the  current  required  to  operate  the  safety  device  to  three  or  four 
amperes.  The  circuits,  both  that  improperly  charged  and  the  safe- 
ty circuit,  lead  to  the  same  brush  of  the  motor.  The  former  in- 
cludes the  resistance  G'  which,  with  the  maximum  resistance  in  the 
lines,  reduces  the  current  in  the  field  F'  to  one-fifth  that  in  the 
field  F. 

It  will  be  noticed  that,  in  this  method  as  in  that  previously 
described,  the  action  of  the  safety  device  depends  on  the  continuity 
of  a  wire.  In  this  case  it  is  the  wire  which  was  last  used  in  operat- 
ing the  switch  and  which  must  have  been  good  when  the  last  move- 
ment was  made.  The  two  methods  are,  therefore,  equal  in  the  de- 
gree of  jsafety  afforded.  There  is  one  point  of  difference  that  may 


RAILWAY  SIGNALING 


47 


be  worth  mentioning.  The  safety  device  shown  in  Fig.  24,  when  it 
becomes  operative,  affects  only  the  switch  to  which  it  is  connected, 
while  that  shown  in  Fig.  23  throws  the  whole  plant  out  of  service, 
or  as  much  of  it  as  is  connected  to  one  common  return.  If  the  cir- 
cuit breaker  T  is  cut  into  the  common  instead  of  the  main  positive 
lead,  and  one  cut-out  is  provided  for  each  common  return,  then 
when  one  of  them  is  opened  by  an  improper  connection,  only  that 
part  of  the  plant  served  by  that  common  return  is  put  out  of  ser- 
vice. Obviously,  this  principle  could  be  extended,  so  as  to  cut  out 
only  one  switch,  by  using  a  separate  return  for  each  switch  instead 
of  a  common  wire,  and  by  putting  a  cut-out  in  each  return. 


FIG.   25 — VIEWS   OF   ELECTRIC   INTERLOCKING    MACHINE   SHOWING  END  AND 
FRONT   ELEVATION 


After  what  has  been  written  in  preceding  articles  descriptive 
of  interlocking  apparatus,  an  extended  description  of  the  apparatus 
used  in  connection  with  the  all-electric  system  is  unnecessary.  A 
brief  description  of  the  more  important  parts  peculiar  to  the  electric 
system  may,  however,  be  of  interest. 

An  interlocking  machine  now  in  quite  extensive  use,  is  shown 
in  Fig.  25.  This  resembles,  in  general  appearance,  the  electro-pneu- 
matic machine  already  described.  The  only  difference  is  in  the  indi- 
cation apparatus  which,  for  the  electric  machine,  is  adapted  to  the 
alternating  current  described  in  connection  with  Fig.  22.  The  indica- 
tion motor  has  its  armature  shaft  in  a  vertical  position,  to  which  is 


48 


RAILWAY  SIGNALING 


attached  a  piece  of  centrifugal  apparatus  very  similar  in  construction 
to  the  well  known  form  of  governor  used  on  the  steam  engine.  The 
rapid  rotation  of  the  armature  causes  the  weights  to  separate,  and 
through  a  system  of  levers,  to  lift  the  indication  latch  and  release 
the  lever.  This  mode  of  construction  makes  it  necessary  to  have 
a  very  rapid  rotation  of  the  indication  motor  armature  to  produce 
the  desired  effect,  and  this  rotation  can  be  secured  only  by  a  rapid 
succession  of  alternating  impulses  in  the  coils  of  the  motor.  A  di- 


ne.  26  AND  27 — PLAN   AND  ELEVATION  SHOWING  ELECTRIC  SWITCH  AND  LOCK 

MOVEMENT 

rect  current  through  these  coils  has  no  effect  other  than  to  lock 
the  armature  against  rotation. 


SWITCH  AND  LOCK   MECHANISM 

Fig.  26  is  a  plan  and  Fig.  27  a  side  elevation,  showing  a  switch 
and  its  operating  mechanism.  The  switch  and  lock  movement  is 
driven  by  a  direct-current  motor  of  about  1.5  hp,  designed  to  be 
operated  at  no  volts.  The  shaft  of  this  motor  is  connected  by  means 
of  a  magnetic  clutch  to  a  shaft  extension  in  the  same  line,  working 
a  cam  drum,  which  operates  the  switch  and  lock.  Intermediate 
between  the  magnetic  clutch  and  drum,  there  is  a  reduction  gearing 


RAILWAY  SIGNALING  49 

with  a  speed  ratio  of  twenty-five  to  one.  It  will  be  noticed  that 
there  are  two  cams  on  the  drum,  one  of  these  working  the  lock  rod 
and  detector  bar,  and  the  other  the  switch,  connection  being  made 
to  the  detector  bar  and  switch  through  cranks.  The  lock  is  worked 
direct  by  a  straight  bar  which  slides  longitudinally  underneath  the 
car..,  motion  being  imparted  by  means  of  a  lug  fitting  the  cam  slot. 
It  will  be  noticed  that  in  each  case  the  cam  slot,  for  a  portion  of  its 
travel,  moves  in  a  plane  at  right  angles  to  the  shaft,  so  that  while 
that  portion  is  passing  the  hub  on  the  driving  bar  or  crank,  no 
movement  of  the  latter  takes  place;  it  is  only  while  the  hub  is  en- 
gaged by  the  diagonal  portion  of  this  slot,  that  movement  is  im- 
parted to  the  switch  or  lock  mechanisms.  The  operation  is  there- 
fore on  the  principle  of  the  switch  and  lock  movement,  with  which 
signal  engineers  are  quite  familiar,  and  briefly  is  as  follows :  When 
the  drum  is  revolved  by  the  motor,  the  lock  rod  and  detector  bar 
immediately  begin  to  move,  and  as  soon  as  these  have  completed 
their  stroke,  the  motions  of  these  mechanisms  cease  and  the  move- 
ment of  the  switch  begins.  After  the  switch  has  been  moved  over 
against  the  stock  rail,  further  motion  of  the  lock  bar  locks  the 
switch  and  at  the  same  time  operates  a  knife  switch  which  opens 
the  control  circuits  and  closes  the  indication  circuit. 

A  noticeable  feature  of  this  switch  and  lock  movement  is  the 
arrangement  of  the  parts  in  one  long  and  narrow  mechanism  which 
occupies  but  little  space  between  the  tracks.  For  this  reason  it  can 
be  used  in  many  places  between  tracks  that  come  too  close  together 
to  admit  movements  of  other  design,  which  in  some  places  must  be 
placed  outside  the  tracks  with  long  rod  connections,  passing  under 
intermediate  tracks  to  the  switch.  Another  feature  of  this  design 
worth  noticing,  is  the  fact  that  the  cam  drum  is  reversible,  so 
that  the  movement  can  be  operated  either  right  or  left,  merely  by 
changing  the  drum  end  for  end,  the  position  of  the  motor  and 
clutch  remaining  the  same.  The  motor,  clutch,  and  drum  are  all 
attached  to  a  steel  base  plate. 

Returning  now  to  the  motor  part  of  the  movement;  the  direc- 
tion of  rotation  for  reversing  the  switch  is  controlled  by  means  of 
a  double  field  winding,  one  part  of  which  is  cut  out  while  the  other 
is  in  circuit.  When  the  switch  is  to  be  thrown  in  the  reverse  direc- 
tion, the  lever  on  the  interlocking  machine  merely  changes  the  con- 
nection of  the  operating  circuit  to  the  other  field  winding. 

The  use  of  the  magnetic  clutch  is  an  advantage  in  several  ways. 
It  permits  the  breaking  of  the  motor  connection  with  the  throwing 


50  RAILWAY  SIGNALING 

mechanism  instantly  and  at  the  proper  time,  and  the  absence  of  a 
rigid  connection  prevents  breaking  or  straining  of  the  parts  if  the 
movement  of  the  switch  should  become  blocked,  as  by  the  dropping 
of  a  lump  of  coal  or  other  obstruction.  The  blocking  of  the  switch 


FIG.  28 — SIDE  ELEVATION  OF  SOLENOID  SAFETY  CIRCUIT  CONTROLLER  FOR 
SWITCH    MOVEMENT 

merely  causes  the  clutch  to  slip  until  a  fuse  is  blown  on  the  inter- 
locking machine.  It  should  here  be  noted  that  the  motion  of  the 
switch  follows  the  lever.  If  the  switch  is  found  to  be  blocked,  it 
can  be  thrown  back  by  simply  reversing  the  lever. 


SAFETY  CONTROLLER  FOR  SWITCHES 

The  safety  controller  used  with  the  system  shown  in  Fig.  24, 
and  which  automatically  cuts  out  a  switch  motor  if  the  lines  be- 


FIG.  29 — PLAN  VIEW  OF  CIRCUIT  CONTROLLER 


come  improperly  connected,  combines  in  one,  the  functions  ot  two 
electro-magnetic  circuit  controllers.  The  function  of  one  is  to  open 
the  motor  circuit  when  the  lever  movement  is  completed,  and  of  the 
other  to  open  the  next  operating  circuit  when  it  is  energized  by  con- 


RAILWAY  SIGNALING 


FIG.    3O — END   ELEVATION    OF   CIRCUIT 
CONTROLLER 


nected  wires,  and  thus  to  prevent  a  wrong  movement.  The  instru- 
ment which  is  illustrated  in  Figs.  28,  29,  30  and  31  comprises  two 
solenoids  A  and  A,  fixed  to  a  cast  iron  base  V.  Each  solenoid  has 
a  moveable  core  D,  connected  by  means  of  a  jaw  E  to  a  lever 

F.  The  lever  F  is  pivoted  at 
its  middle  to  a  fixed  support 
G  and  is  connected  at  its  up- 
per end  to  a  rod  H,  free  to 
move  longitudinally.  The  rod 
H  carries  a  contact  bridge  I, 
which  will  connect  the  contact 
points  /  and  K  when  the  core 
D  is  drawn  into  the  sole- 
noid, and  will  connect  the 
contact  points  L  and  M 
when  the  core  D  is  drawn  out- 
ward. The  levers  F  and  F'  are 
connected  near  the  lower  ends 
by  a  spring  Z,  which  causes  the  bridge  /'  to  connect  L'  and  M', 
when  the  core  D  is  drawn  into  its  solenoid  A  to  nearly  the  full  ex- 
tent. Similarly  the  contact  bridge  /  is  made  to  connect  L  and  M 
when  the  core  D'  is  drawn  into  the  solenoid  A'.  The  contacts 
/  and  K  are  carried  by  the  slate  block  N,  with  springs  interposed 
so  that  they  may  be  pushed  in  about  three-sixteenths  of  an  inch. 
The  contacts  L  and  M  are  fixed  to  the  slate  block  O.  The  relation 
of  the  parts  is  such,  that  the  bridge  /  touches  the  contacts  /  and  K, 
while  the  core  D  is  still  three-six-  

X  X 

teenths  of  an  inch  from  its  complete 
forward  stroke,  and  the  bridge  /' 
touches  L'  and  M'  with  the  core  D 
about  one-sixteenth  of  an  inch  from  its 
full  inward  stroke.  These  clearances 
are  allowed  for  making  good  contact. 
Each  solenoid  has  two  coils  of  wire. 
The  coil  C  has  100  turns  of  No.  13  B.  & 
S.  gauge  and  the  coil  B,  I  100  turns  of  No.  15  B.  &  S.  gauge.  The 
resistance  coils  U  and  C/',  each  of  twenty  ohms,  are  in  series  with 
the  coils  B  and  B'  at  the  starting  of  a  movement,  and  the  circuits  in- 
cluding them  may  be  called  the  starting  circuits.  The  coil  B  is  con- 
nected to  terminals  P  and  Q,  and  the  coil  C  is  connected  to  term- 
inals R  and  S. 


FIG.    31 — WIRING   DIAGRAM 


52  RAILWAY  SIGNALING 

At  the  beginning  of  a  movement,  current  flows  through  coils 
C,  B,  and  U  in  series,  and  draws  in  the  core  D,  causing  the  bridge 
/'  to  connect  L'  and  M',  which  shunts  the  coils  B  and  U,  so  that 
the  operating  and  indicating  currents  flow  only  through  the  coil  C, 
of  a  very  low  resistance,  but  having  sufficient  turns  to  hold  the  core 
D  in  place.  The  bridge  /  will  touch  /  and  K  before  I'  touches  L' 
and  Mr,  so  that  if  the  current  happened  to  come  from  a  foreign 
source  without  the  lever  having  been  moved,  current  would  also 
flow  from  the  last  operating  wire,  which  is  still  in  connection  with 
battery,  through  coils  C ,  B',  bridge  I,  and  the  motor,  and  would 
hold  /'  away  from  L'  and  M',  by  drawing  in  the  core  D'.  This  cur- 
rent will  run  the  motor  light  in  the  direction  it  ran  in  making  the 
last  movement,  and  without  energizing  the  clutch.  The  contact  K 
is  provided  with  a  head  on  its  inner  end,  which  makes  connection 
with  a  contact  X,  when  K  is  pushed  outward  by  the  spring,  but 
when  K  is  pushed  in  by  the  bridge  /,  it  is  separated  from  X.  The 
object  of  this  is  to  cause  the  cut-off  current  to  flow  only  through 
the  safety  contacts  /  and  K,  and  thus  afford  a  -test  of  their  condi- 
tion at  each  movement  of  the  switch. 

When  the  core  D  is  drawn  completely  into  the  solenoid  A,  the 
latch  T  drops  into  the  path  of  a  projection  on  the  lever  Fr,  so  that 
if  the  magnet  A'  is  energized  while  A  is  still  holding  its  core,  the 
core  D'  will  be  stopped  by  the  latch  T  before  it  puts  the  bridge  /' 
against  /'  and  K'.  A  similar  latch,  T,  stops  the  core'D  under  sim- 
ilar conditions.  These  latches  come  into  play  in  the  action  of  the 
cut-off  current.  If  in  that  case  the  bridge  /'  were  allowed  to  move 
far  enough  to  touch  /'  and  K',  the  safety  circuit  would  be  tem- 
porarily closed  and  cause  sparking  at  the  contacts. 


CHAPTER  IV 

THE  ELECTRIC  TRAIN  STAFF  SYSTEM 
DEVELOPMENT 

THE  electric  train  staff  system  of  to-day  is  a  gradual  develop- 
ment from  a  simple  principle  for  the  operation  of  railroads 
which  was  recognized  in  England  as  early  as  1840 ;  namely, 
that  to  safely  pass  over  a  given  section  of  single  track,  every  train 
should  have  in  its  possession  a  tangible  right  to  do  so  in  the  form  of 
some  specific  article  of  which  there  is  only  one  obtainable.  The  first 
train  staff  was  a  metal  bar  about  two  feet  long,  which  had  cast  or 
engraved  on  it  the  name  of  the  two  stations  between  which  it  alone 
gave  authority  for  any  train  to  proceed.  Unless  trains  moved  alter- 
nately in  opposite  directions  the  staff  had  to  be  returned  over  the  sec- 
tion by  a  special  engine  or  in  some  cases  by  road. 

To  partially  overcome  this  difficulty  the  staff  and  ticket  system 
was  devised,  in  which  device  the  original  staff  became  a  key  that 
would  unlock  a  box  at  either  end  of  the  section  and  permit  tickets 
to  be  taken  therefrom.  If  it  was  desired  to  forward,  say  three  trains 
from  one  station  to  another  before  one  should  proceed  in  the  opposite 
direction,  the  ticket  box  was  unlocked  by  the  staff  and  a  ticket  given 
to  the  first  and  second  trains,  the  third  train  receiving  the  staff. 

Since  an  engineer  or  guard  of  any  train  when  receiving  a  ticket 
was  required  to  see  the  staff  as  well,  this  system,  while  making  head- 
on  collisions  impossible,  did  not  permit  trains  to  enter  a  section  from 
the  end  at  which  the  staff  did  not  happen  to  be.  To  accomplish  this 
result,  Mr.  Edward  Tyer,  in  1878,  introduced  his  electric  tablet  ap- 
paratus, which  consisted  of  two  instruments,  one  at  either  end  of  a 
section,  each  instrument  containing  a  certain  number  of  tablets  any 
one  of  which  constituted  the  right  of  a  train  to  pass  over  that  section. 
The  two  instruments  were  electrically  connected  and  synchronized  so 
that  the  removal  of  a  tablet  from  either  instrument  absolutely  pre- 
vented any  other  being  taken  out. 

In  1889  Mr.  Webb,  the  chief  mechanical  engineer,  and  Mr. 
Thompson,  the  signal  superintendent  of  the  London  &  Northwestern 
Railway,  invented  the  Webb  &  Thompson  electric  train  staff,  in 
which  staffs  were  substituted  for  the  tablets  in  the  Tyer  system  and  a 
permissive  feature  added  whereby  several  trains  could  follow  each 


54.  RAILWAY  SIGNALING 

other  into  a  block  section  if  desired,  in  a  manner  similar  to  that  em- 
ployed in  the  non-electric  staff  and  ticket  system. 

The  first  installation  of  the  Webb  &  Thompson  system  was  made 
with  eminently  satisfactory  results  in  May,  1894,  on  the  Chicago, 
Milwaukee  and  St.  Paul  Railway  between  Savanna,  111.,  and  Sabula, 
Iowa,  and  is  described  herewith : 

APPLICATION  OF  TRAIN  STAFF  SYSTEM  * 

"The  lines  of  the  Southern  district  of  the  Chicago,  Milwaukee  & 
St.  Paul  Railway  cross  the  Mississippi  river  between  Savanna,  Illi- 
nois, and  Sabula,  Iowa.  The  distance  between  these  two  stations  is 
three  miles,  and  there  is  one  grade  crossing,  one  draw  bridge,  and 
one  local  station  in  the  block.  Over  this  track,  which  is  single,  the 
traffic  of  about  three  thousand  miles  of  the  St.  Paul  company's  lines 
passes.  These  lines  extend  directly  to  Kansas  City,  Omaha,  Sioux 
City  and  Chamberlain  on  the  west,  and  to  Chicago,  Milwaukee  and 
Racine  on  the  east.  During  the  larger  part  of  the  year  the  traffic  is 
heavy  (the  bridge  block  being  the  neck  of  the  bottle,  so  to  speak) 
and  rarely  falls  below  fifty  trains  per  day  at  any  time. 

The  division  yard  is  located  at  Savanna,  on  the  east  side  of  the 
Mississippi  river,  making  it  necessary  for  the  trains  of  both  divisions 
west  of  the  river  to  use  the  bridge  block,  and,  moving  the  traffic  from 
so  large  a  territory,  it  is  to  be  expected  that  they  will  be  irregular  in 
number,  and  that  they  will  bunch  during  certain  hours.  The  use  of 
a  time  table  showing  the  trains  over  the  river  block  was  abandoned, 
because  it  was  found  impossible  to  arrange  it  so  that  it  was  a  reason- 
ably correct  exhibit  of  the  traffic.  Nor  was  it  possible  to  move  the 
trains  through  the  dispatchers  of  either  division,  as  the  work  on  their 
respective  divisions  would  not  permit  the  close  attention  to  the  bridge 
block  which  the  nature  of  the  service  demanded.  For  a  time  in  the 
early  history  of  the  bridge  this  was  done,  but  the  work  was  finally 
put  in  the  hands  of  the  operators  at  each  end  of  the  block.  It  was 
found  to  be  necessary  to  use  some  other  than  the  ordinary  dispatching 
systems.  That  was  found  to  be  too  slow  and  cumbersome  to  meet 
the  requirements  of  the  quick  work  necessary  under  the  conditions 
constantly  arising  incident  to  unexpected  delays,  and  to  increase 
or  decrease  of  traffic.  To  meet  the  conditions  described  a  train 
order  by  card  system  was  adopted,  which  was  in  successful  use  for 


*From  a  paper  read  before  the  Western  Railway  Club  by  Mr.  C.  A. 
Goodwin,  at  that  time  superintendent  of  the  Chicago,  Milwaukee  &  St.  Paul 
Railway. 


RAILWAY  SIGNALING  55 

many  years.  It  was  virtually  a  staff  system — the  card  representing 
the  staff — but  it  lacked  one  element:  it  was  impossible  to  interlock 
the  cards.  As  traffic  increased,  and  increased  acceleration  of  trains 
became  necessary,  it  was  apparent  that  the  company  would  be  com- 
pelled to  either  double-track  the  bridge  block  or  find  some  unobjec- 
tionable way  of  handling  the  trains.  Owing  to  the  character  of  the 
country  the  construction  of  a  second  track  would  have  been  very  ex- 
pensive, and  the  selection  of  a  satisfactory  system  for  handling  the 
traffic  became  the  subject  of  much  thought  and  investigation.  After 
a  thorough  examination  and  inquiry  the  Webb-Thompson  electric 
staff  system,  largely  in  use  on  the  London  &  North- Western  Railway 
and  in  Australia,  was  adopted  and  placed  in  service  in  May,  1894. 
This  was  the  first  installation  of  the  staff  system  in  the  United  States, 
and  probably  in  either  of  the  Americas. 

"From  the  preceding  brief  description  it  is  clear  that  with  this 
system  the  bridge  dispatcher  has  no  responsibility  except  to  give  the 
proper  trains  the  preference.  He  may  delay  traffic,  but  he  cannot 
create  a  condition  of  danger.  It  is  not  necessary  for  him  to  provide 
for  a  proposed  or  supposed  movement  of  trains  by  sending  numerous 
orders,  only  to  find  it  necessary  to  cancel  them  because  the  train  can- 
not move  as  expected.  He  is  in  touch  with  the  yardmaster  at  Sa- 
vanna and  with  the  dispatcher  at  both  divisions,  and  through  these 
sources  is  fully  informed  in  regard  to  the  probable  movement  of 
trains  in  both  directions.  He  may  have  expected  to  hold  a  freight 
train  for  a  passenger  train,  which  is  reported  on  time  at  some  distant 
station,  only  to  find  that  the  passenger  train  has  lost  time  and  that  he 
can  just  squeeze  the  freight  train  into  the  terminus.  There  is  no  ne- 
cessity for  sending  hurried  orders  with  attendant  possibility  of  errors. 
He  simply  signals  for  a  staff,  and  in  five  seconds  or  less  the  engineer 
has  his  authority  to  go  forward.  Or  supposing  the  situation  revers- 
ed. A  passenger  reported  late  has  made  up  so  much  time  that  an- 
other train  which  is  approaching,  and  for  which  a  staff  has  been 
withdrawn,  cannot  go  forward.  Transportation  men  know  the  delay 
which  results  when  it  is  necessary  to  change  or  make  void  telegraphic 
orders.  No  such  delays  occur  with  the  staff  system.  It  is  only 
necessary  to  leave  the  signal  at  danger,  replace  his  staff  in  the  in- 
strument (enabling  one  to  be  withdrawn  at  the  other  end  of  the 
block,)  and  the  passenger  train  goes  forward  with  no  loss  of  time. 
In  case  of  there  being  so  great  a  delay  to  a  train,  to  which  a  staff  has 
been  delivered,  that  it  is  desired  to  recall  its  permission  to  move,  the 
staff  is  brought  back  to  the  office  and  replaced  in  the  instrument, 


56  RAILWAY  SIGNALING 

thereby  cancelling  its  authority  to  proceed  and  in  a  manner  which 
cannot  be  misunderstood. 

"When  a  work  train  is  to  occupy  the  block  the  delivery  of  a  staff 
means  that  it  is  to  be  protected  in  both  directions,  and  that  no  flag- 
man need  be  sent  out,  delaying  fifty  or  a  hundred  men  while  he  comes 
in. 

"These  few  examples  of  the  many  complications  that  must 
necessarily  arise  in  the  handling  of  traffic  on  a  single  track  are  cited 
to  illustrate  the  facility  with  which  the  staff  system  does  its  train  dis- 
patching ;  its  possibilities  in  connection  with  the  movement  of  trains 
on  single  track,  and  its  especial  adaptability  to  short  stretches  of  track 
used  by  the  trains  of  several  divisions  or  different  railways,  as  com- 
pared with  the  telegraphic  movement ;  the  advantage  both  as  regards 
safety  and  facility  of  handling  being  distinctly  with  the  staff  system. 

"It  is  not  the  intention  to  decry  our  system  of  train  dispatching. 
There  can  be  no  question  but  what  it  is  a  most  economical  and  satis- 
factory method  of  handling  traffic  under  ordinary  conditions  with 
not  too  heavy  a  train  movement ;  but  we  are  obliged  to  admit  that  the 
system  is  open  to  objections  which  particularly  relate  to  safety  as  well 
as  facility,  "t he  staff  system  is  capable  of  extended  application.  It 
is  at  once  a  block  signal,  a  train  dispatcher  and  a  time  table.  It  is 
to  the  movement  of  trains  between  stations  what  the  interlocking  of 
switches  and  signals  is  at  stations  and  grade  crossings." 

The  main  objection  to  the  extended  adoption  of  the  Webb  & 
Thompson  apparatus  was  the  size  of  the  staff,  which  made  it  difficult 
to  catch  at  high  speed.  To  overcome  this  objection,  a  new  design 
was  introduced  in  1900, -known  as  the  high  speed  train  staff  system, 
which  was  based  on  the  same  general  principles  and  method  of 
operation  as  the  Webb  &  Thompson,  but  possessed  the  essential  ad- 
vantage of  employing  staffs  only  six  inches  in  length,  weighing  six 
and  one-half  ounces ;  as  against  staffs  twenty-two  inches  long,  weigh- 
ing four  pounds,  of  the  Webb  &  Thompson  system,  thus  greatly 
simplifying  the  problem  of  taking  the  staff  at  high  speeds. 

On  the  Atchison,  Topeka  &  Santa  Fe  Railway,  among  other 
places,  it  was  applied  to  a  section  extending  from  Trinidad,  Colo- 
rado, to  Raton,  New  Mexico,  a  distance  of  25  miles,  which  was  di- 
vided into  seven  block  sections.  This  portion  of  the  Atchison  com- 
prises mountain  grades  averaging  three  and  one-half  percent  for  a 
greater  part  of  the  distance,  over  which  a  traffic  of  approximately 
60  trains  a  day  is  operated.  On  account  of  the  number  of  trains, 
and  also  from  the  fact  that  each  train  required  two  and  sometimes 


RAILWAY  SIGNALING  57 

three  engines  on  the  up-grade,  an  average  of  one  hundred  and  fifty 
train  orders  was  issued  in  each  twenty-four  hours,  most  of  which 
were  sent  to  not  less  than  two  stations,  so  that  the  total  delay  to  trains 
awaiting  these  orders  can  easily  be  imagined.  With  the  introduc- 
tion of  the  staff  system  as  many,  or  more,  trains  have  since  been 
handled  over  this  section  with  no  collision  and  a  minimum  of  delays. 
At  the  intermediate  stations  on  this  section,  staff  cranes  are  provided 
from  which  the  enginemen  can  take  the  staffs  at  a  speed  up  to  25 
miles  an  hour  without  the  use  of  any  special  attachments  on  the  en- 
gine. 

The  latest  type  of  staff  instrument,  known  as  the  electric  high- 
speed train  staff,  Model  No.  2,  has  been  developed  during  the  past 
four  years,  and  employs  practically  the  same  size  and  weight  of  staff 
as  the  Model  No.  I  machine,  over  which  it  possesses  the  following 
advantages:  By  having  separate  drums  for  putting  in  and  taking 
out  the  staffs,  equal  wear  on  all  staffs  is  secured;  whereas,  in  the 
earlier  instrument  some  of  the  staffs  would  be  practically  worn  out 
from  constant  use,  while  others  were  hardly  ever  used  at  all.  The 
second  advantage  lies  in  the  special  type  of  indicator  employed  in 
this  machine,  which  plainly  shows  the  operator  by  the  display  of  a 
white  or  red  disc  whether  or  not  his  instrument  is  in  condition  for 
him  to  remove  a  staff,  and  thus  leaves  him  no  excuse  for  unduly 
forcing  the  mechanism.  Numerous  other  improvements  exist  in 
this  type  of  machine,  but  they  consist  principally  in  minor  details  of 
construction. 

'  ,  An  installation  of  this  type  has  been  in  operation  over  fifteen 
months  on  a  section  of  the  Southern  Pacific  Railway  between 
Truckee,  California,  and  Colfax,  California,  a  distance  of  98  miles, 
divided  into  37  blocks.  This  portion  of  the  Southern  Pacific  is  in 
the  Sierra  Nevada  mountains  and  14  of  the  staff  stations  are  located 
in  the  snow  sheds,  of  which  there  are  nearly  40  miles. 

PRINCIPAL  ADVANTAGES  OF  THE  ELECTRIC  TRAIN  STAFF  SYSTEM 

While  in  the  foregoing  the  general  principles  on  which  the  elec- 
tric train  staff  is  operated  have  been  described,  yet  particular  atten- 
tion is  called  to  the  following  points : 

First — The  electric  train  staff  system  may  be  considered  as  a 
mechanical  assistant,  which  issues  metal  train  orders  under  the  gen- 
eral direction  of  the  train  despatcher,  giving  trains  the  right  to  pro- 
ceed over  certain  sections  of  track,  and  will  only  issue  one  such 
order  at  one  time  for  any  section,  except  in  the  case  of  following 


58  RAILWAY  SIGNALING 

trains  where  the  permissive  feature  is  used,  thus  obviating  all  dan- 
ger of  "lap  orders." 

Second — In  place  of  eliminating  the  train  despatcher,  as  has  at 
times  been  erroneously  supposed,  the  train  staff,  by  removing  all 
dangers  of  collision  and  doing  away  with  all  train  orders,  relieves 
his  mind  from  the  constant  strain  imposed  upon  it  under  the  present 
system  and  thus  gives  him  ample  time  to  issue  orders  to  operators 
on  his  division  for  the  proper  movements  of  the  trains  under  his 
control. 

Third — It  avoids  all  the  delay  now  experienced  in  waiting  for 
train  orders.  If  conditions  are  right  for  a  train  to  proceed  the  staff 
can  be  obtained  immediately  and  when  the  permissive  system  is  em- 
ployed trains  can  follow  each  other  as  closely  as  the  rules  of  the  road 
permit. 

Fourth — It  alone  of  all  block  systems  provides  a  tangible  piece 
of  evidence  in  the  shape  of  the  staff  to  the  engineer  or  conductor  of 
his  right  to  the  particular  block  section  he  may  occupy. 

Fifth — It  can  be  surrounded  with  all  such  additional  safeguards 
as  conditions  and  locations  may  warrant,  including  semaphore  sig- 
nals and  continuous  track  circuit,  electric  locks,  etc. 

Sixth — It  can  be  safely  operated  by  any  railroad  employee  of 
average  intelligence.  A  knowledge  of  telegraphy  is  not  necessary 
for  its  operation. 

Seventh — At  stations  where  telegraph  operators  are  employed 
who  have  other  duties,  it  is  found  that  the  operation  of  the  staff  takes 
up  considerably  less  of  their  time  than  is  now  expended  on  tele- 
graphic train  orders. 

Eighth — In  most  installations,  the  absolute  staff  system  is  em- 
ployed which  permits  but  one  staff  to  be  out  of  any  pair  of  machines 
at  one  time  and  consequently  allows  but  one  train  in  a  block. 

In  a  number  of  cases,  however,  where  the  blocks  are  of  neces- 
sity long  and  traffic  is  heavy  through  certain  portions  of  the  day,  the 
permissive  feature  is  introduced  which,  while  it  makes  it  impossible 
for  two  trains  proceeding  in  opposite  directions  to  be  in  any  given 
block  at  one  time,  permits  as  high  as  twelve  trains  to  follow  each 
other  in  the  same  block  at  close  intervals. 


RAILWAY  SIGNALING  59 

ABSOLUTE  STAFFS  AND  STAFF  INSTRUMENTS 

In  the  operation  of  the  electric  train  staff  the  track  to  be  pro- 
tected is  divided  into  blocks  or  sections  of  such  length  as  to  best 
accommodate  local  and  traffic  conditions.  These  blocks  usually  ter- 
minate at  existing  stations  or  telegraph  offices,  though  occasionally, 
as  in  the  telegraph  block  system,  additional  block  stations  have  to  be 
installed  when  the  distance  betwen  any  two  existing  stations  is  too 
great  for  the  expeditious  handling  of  traffic. 

Each  section  is  controlled  by  two  instruments  of  the  type  shown 
in  Fig.  32,  one  at  each  end  of  the  section,  which  for  convenience  in 
this  description  are  referred  to  as  "X"  and  "Y."  Each  instrument 
is  equipped  with  a  sufficient  number  of  staffs  (varying  from  10  to 
35  per  section)  to  take  care  of  the  traffic  conditions.  No  train  is 
permited  to  proceed  between  X  and  Y  in  either  direction  unless  the 
conductor  or  engineer  has  in  his  possession  one  of  these  staffs  which 
is  in  effect  a  metal  train  order.  The  instruments  at  X  and  Y  are 
electrically  connected  and  synchronized  so  that  the  withdrawal  of  a 
staff  from  either  can  only  be  effected  by  the  joint  action  of  the  opera- 
tors at  X  and  Y,  and  but  one  staff  can  be  out  of  both  instruments  at 
any  one  time. 

To  move  a  train  from  X  to  Y  the  manipulation  of  the  instru- 
ments is  as  follows :  The  operator  at  X  presses  bell  key  A,  Figs. 
32  and  34  the  number  of  times  prescribed  in  the  bell  code,  which  rings 
bell  L,  Figs.  33-4  at  Y  through  circuit  I,  2,  3,  4,  5,  6,  7,  8,  9,  10,  u, 
12,  13,  14,  15,  16,  17,  18.  The  operator  at  Y  first  acknowledges 
receipt  on  his  bell  key  by  ringing  bell  L  (Figs.  33-4)  at  X  (through 
circuit  10,  20,  21,  8,  7,  6,  5,  4,  22,  23,  24,  25,  17,  16,  15,  14,  13,  26,) 
and  then  holds  it  closed,  thereby  deflecting  the  "current  in- 
dicating needle"  F  at  X  (Figs.  32-34)  to  the  right.  This  in- 
forms X  that  Y  has  furnished  X  current  and  he  proceeds  to 
remove  the  staff  by  turning  the  preliminary  handle  B  Fig.  32 
to  the  right  as  far  as  it  will  go,  which  raises  the  armature  J 
Fig.  33  up  to  the  magnets  K  (Fig.  33)  transferring  the  cur- 
rent from  the  bell  L  to  the  coil  K88  (Fig.  34)  through  the 
circuit  10,  20,  21,  8,  7,  6,  5,  4,  22,  23,  27,  28,  25,  17,  16,  15,  14,  13, 
26,  and  at  the  same  time  closing  the  circuit  on  coil  K  360  (Fig.  34) 


6o 


RAILWAY  SIGNALING 


through  the  circuit  I,  2,  29,  50, 
28,  25,  18,  after  which  the  pre- 
liminary spindle  handle  B  (  Fig. 
32)  is  permitted  to  automatical- 
ly return  to  its  normal  position. 
This  unlocks  the  revolving  drum 
C  (Figs-  33  and  35)  and  indi- 
cates the   fact  by  displaying  a 
white  instead  of  a  red  disc  in  the 
indicator  at  F  (Fig.  32).     The 
operator    now    moves    the    end 
staff  E  (Fig.  32)  up  the  vertical 
slot  into   engagement  with   the 
drum  C,   (Figs.  33  and  35)  the 
outer  guard  TV  (Fig.  32)  having 
first  been  turned  to   the   right 
position;     revolves     the     latter 
through  half  a  turn,  using  the 
staff    as   a   handle,    and   finally 
withdraws  the  staff  through  the 
opening  at  M    (Fig.   32).      In 
making  the  half  turn,  the  drum 
C  has  reversed  the  polarity  of 
the  operating  current,  thereby 
throwing  the  instruments  at  X 
and  Y  out  of  synchronism  with 
each    other,    and    moving    the 
"staff  indicating  needle"  G  at  X 
(Fig.   35)    from  "Staff  In"  to 
"Staff   Out."     Immediately    on 
withdrawing   the   staff   the  op- 
erator at  X  once  more  presses 
his  bell  key  A,  which  indicates 
to  the  operator  at  Y  by  moving 
his  needle   from  "Staff  In"  to 
"Staff  Out"  that  the  operation 
is  completed.    A  side  view  of  a 
staff  instrument  with  the  outer 
case     removed     is     shown     in 


FIG.    32  —  STAFF    INSTRUMENT    SHOWING  =>      ° 

TRAIN  STAFFS,  REVOLVING  PLATE,  IN-  The  staff  withdrawn  is  now 

DICATING      DIAL,     SIGNALING     BUTTON,  ddivered  tQ  thfi  trajn  by  hand  jf 
ETC. 


RAILWAY  SIGNALING 


61 


FIG.   33 — BACK  VIEW  OF   STAFF   INSTRUMENT   SHOWING   MECHANISM 


62 


RAILWAY  SIGNALING 


the  train  is  at  rest  or  passing  at  a  speed  less  than  25  miles  per  hour. 
For  higher  speeds  the  staff  is  placed  in  a  special  holder  and  delivered 
by  methods  similar  to  those  followed  in  the  railway  mail  service,  the 
engine  being  fitted  with  a  catcher  and  deliverer.  A  glance  at  the  ac- 
companying cuts  (Figs.  37  and  38)  will  make  this  clear.  As  men- 
tioned before,  in  taking  out  a  staff,  the  polarity  of  the  operating  cur- 
rent is  reversed.  This  prevents  a  second  staff  from  being  taken  out 
of  either  instrument,  as  may  be  noted  from  the  following. 

The  polarity  of  the  local  current  flowing  through  magnet  K  jdo 
(Fig.   34)    is  never  changed,   the  polarity  of  the  current  flowing 


Polarized  Indicator 


FIG.    34 — DIAGRAM    OF    CONNECTIONS    FOR    SIGNALING,    INDICATING    AND    OPERATING 
CIRCUITS    FOR  ONE   BLOCK    SECTION 

through  K  88  (Fig.  34)  is  changed  each  time  a  staff  is  put  in  or  taken 
out  of  either  instrument.  This  puts  the  instruments  either  in  or  out 
of  synchrony.  The  magnet  K  (Fig.  34)  is  formed  of  two  separate 
coils,  one  energized  by  the  local  and  one  by  the  line  battery.  The 
construction  of  this  magnet  is  such  that  when  the  currents  in  both 
coils  run  in  the  same  direction,  the  lines  of  force  flow  around  the 
cores  and  connecting  straps,  thus  forming  no  point  of  attraction  for 
the  armature.  When  the  current  is  reversed  in  one  coil,  however, 


RAILWAY  SIGNALING 


the  lines  of  force  oppose  each  other  and  the  armature  being  brought 
to  the  point  of  attraction  is  held  there.  With  the  staff  out,  the  cir- 
cuits are  as  follows : — starting  from  the  -)-  side  of  battery  at  Y, 
(Fig.  34),  through  ip,  20,  21,  Bell  Key  A  closed,  8.  7,  6,  5,  17,  25,  24, 
23,  22,  4,16,  15,  14,  13,  26,  to — side  of  battery  at  Y.  If  an  attempt  be 

made  to  release  a  staff 
by  turning  the  pre- 
liminary handle,  the 
operating  current 
would  be  transferred 
from  the  bell  L  to 
coil  K88  (Fig.  34) 
through  /o,  20,  21, 
bell  key  A  (at  Y) 
closed,  8,  7,  6,  5, 
17,  25,  28,  27,  23,  22, 
4,  16,  15,  14,  13,  26 
to — side  of  battery  at 
Y.  By  comparing  this 
circuit  with  the  one 
described  for  releas- 
ing a  staff,  it  will  be 
seen  that  in  the  for- 
mer the  currents  flow- 
ing through  coils  K 
360  and  88  (Fig.  34) 
oppose  each  other 
and  in  the  latter  they 
do  not,  which  pre- 
vents the  releasing  of 
a  staff. 

On    arrival    of   the 
train    at    Y  the   staff 
is  delivered  either  by 
FIG.  35— FRONT  VIEW  OF  STAFF  INSTRUMENT  WITH    hand  or    deliverer   to 

STAFF    INSERTED    IN    DRUM    AND    OUTER    GUARD  , 

By  rotating  to  position  shown  in  Fig.  32  the     the     operator,      W  h  O 

staff  may  be  released.  having    seen   that  the 

train  is  complete  by  observing  the  rear  end  markers,  places  the  staff 

in  the  opening  M  (Fig.  32)  of  his  instrument  having  first  turned  the 

outer  guard  N  (Fig.  32)  to  place,  moves  the  staff  into  engagement 

.with  the  drum,  D,  (Fig.  33),  revolves  it  through  one-half  turn,  using 


64 


RAILWAY  SIGNALING 


FIG.    36 — SIDE  VIEW   OF    STAFF   INSTRUMENT 
SHOWING    MECHANISM 


the  staff  as  a  handle  and  al- 
lows it  to  roll  down  the  spi- 
ral. He  then  presses  his 
bell  key  the  prescribed 
number  of  times,  thus  noti- 
fying X  that  the  train  is 
out  of  the  section,  which 
operation  also  moves  the 
"staff  indicating  needle"  at 
X  from  "Staff  Out"  to 
"Staff  In."  The  operator 
at  X  presses  his  bell  key  in 
acknowledgment  and  by  so 
doing  moves  the  "staff  indi- 
cating needle"  at  Y  from 
"Staff  Out"  to  "Staff  In" 
(Fig.  39).  The  machines 
are  now  synchronized  and 
another  staff  can  be  obtain- 
ed from  either  in  the  man- 
ner above  outlined. 

The  staff  being  put  in 
the  instrument  at  Y,  the 
circuits  are  as  follows : 
From  +  side  of  battery  at 
Y  through  ip,  20,  21,  Bell 
key  A  closed  at  Y  through 
8,  14,  15,  16,  4,  22,  23,  24, 
25,  17,  5,  6,  7,  13,  26,  to- 
side  of  battery  at  Y.  Should 
a  release  be  required,  the 
preliminary  spindle  at  X 
would  be  turned  and  cur- 
rent transferred  from  the 
bell  to  magnet  K  88  (Fig. 
34)  through  the  following 
circuit;  from-]- side  of  bat- 
tery at  Y  through  ip,  20, 
21,  Bell  key  closed  at  Y, 
through  8,  14,  15,  16,  4,  22, 
23,  27,  28,  25,  17,  5,  6,  /, 


RAILWAY  SIGNALING 


13,  26,  to — side  of  battery  at  Y.  It  will  be  seen  that  the  current 
flowing  through  magnets  K  360  and  88  are  again  opposing  each  oth- 
er, consequently,  a  staff  can  be  released. 

While  it  takes  some  little  time  to  describe  the  method  of  operat- 
ing the  staff  instruments,  yet  as  a  matter  of  fact,  the  removal  of  a 
staff  actually  takes  less  than  five  seconds  and  the  operation  of  putting 
one  in  an  instrument  less  than  two  seconds  under  ordinary  condi- 
tions. 

The  same  methods  are  followed  at  each  succeeding  staff  station, 


FIG.    37 — APPARATUS    FOR    AUTOMATICALLY    CATCHING    AND    DELIVERING    TRAIN 
STAFFS    SIMULTANEOUSLY   AT    HIGH    SPEED 

but  no  two  adjacent  sections  use  the  same  design  of  staff;  that  is  to 
say,  the  staffs  used  between  X  and  Y  will  not  fit  the  instruments  con- 
trolling the  section  between  Y  and  Z.  Usually  four  different  de- 
signs of  staffs  are  employed  in  actual  practice  to  avoid  any  possibil- 
ity of  their  being  improperly  used. 

PERMISSIVE    FEATURE 

While  the  absolute  system,  where  but  one  train  is  allowed  in  any 
section,  is  the  ideal  arrangement,  yet  cases  occur  where  it  is  desir- 


66 


RAILWAY  SIGNALING 


able  to  allow  several  trains  to  follow  each  other  into  the  block  at 
short  intervals.  This  is  known  as  the  permissive  system,  and  con- 
sists of  an  attachment  (Fig.  40)  to  the  absolute  machine  at  each  end 
of  the  section  with  one  permissive  staff.  An  absolute  staff  is  al- 
ways locked  in  a  permissive  attachment  when  it  does  not  contain 
the  permissive  staff. 

To  operate  this  feature  an  absolute  staff  is  withdrawn  from  the 
instrument  at  X  in  the  usual  manner  and  ifsed  as  a  key  to  unlock  the 
attachment  or  base  (Fig.  40)  containing  the  permissive  staff  (Figs. 


FIG.     38 TRAIN     STAFF    CATCHER    MOUNTED    ON    LOCOMOTIVE    TENDER 

As  used  on  the  Cincinnati,  New  Orleans  &  Texas  Railway  on  their 
fast  express  trains  where  the  staff  has  to  be  caught  at  speeds  frequently 
exceeding  sixty  miles  an  hour. 


41  and  42)  which  is  then  taken  out.  The  opening  of  the  base 
and  the  removal  of  the  permissive  staff  locks  the  absolute  staff 
in  the  permissive  attachment,  there  to  remain  until  the  permis- 
sive staff  is  replaced  at  either  X  or  Y.  The  permissive 
attachment  with  outer  case  removed  is  shown  in  Fig.  44.  The 
permissive  staff  consists  of  a  steel  rod  and  n  removable  rings 


RAILWAY  SIGNALING 


(Fig.  43)  any  one  of  which  authorizes  a  train  to  pass  through  the 
section  to  Y.  If  less  than  12  trains  are  to  follow  each  other,  the 
last  one  takes  all  the  remaining  rings  and  the  steel  rod.  When  all  the 
rings  and  the  rod  are  received  at  Y ,  the  operator  reassembles  them 
into  the  complete  permissive  staff  (Fig.  42)  which  he  then  places  in 
the,  permissive  attachment  or  base  (Fig.  41)  and  locks  it  therein  by 
the  absolute  staff  already  in  the  lock  of  this  attachment.  By  so  do- 
ing he  releases  the  absolute  staff  which  he  restores  to  the  absolute 

instrument  in  the  regular 
manner.  The  machines  are 
now  synchronized  and  a 
movement  can  be  made  with 
the  absolute  staff  in  either 
direction  and  from  Y  to  X 
with  the  permissive. 

If  it  is  again  found  nec- 
essary to  move  several  trains 
from  X  to  Y  under  the  per- 
missive system,  the  permis- 
sive staff  must  be  obtained 
by  Y  as  before  described 
and  forwarded  to  X  as  a 
whole  by  the  first  train  mov- 
ing in  that  direction.  When 
a  train  receives  the  entire 
permissive  staff  it  confers 
the  same  rights  as  does  an 
absolute  staff. 

CONTROL  OF  SIGNALS 

In  its  capacity  as  a  key 
the  absolute  staff  has  a  num- 
ber of  uses  in  addition  to 
that  already  described. 
Where  signals  are  used  to 

indicate  to  an  approaching  train  whether  or  not  it  will  receive  a  staff, 
an  instrument  known  as  the  staff  lever  lock  (Fig.  45)  is  attached  to 
each  lever  operating  such  signals.  To  clear  a  signal  the  staff  after 
being  withdrawn  is  first  used  to  unlock  the  lever  lock  (Fig.  45). 
The  signal  is  then  cleared  and  the  staff  removed  from  the  lock  and 
delivered  to  the  train. 


FIG.  39 — FRONT  VIEW  OF  STAFF  INSTRU- 
MENT WITH  STAFF  READY  TO  ROLL  DOWN 
THE  SPIRAL 


68 


RAILWAY  SIGNALING 


To  insure  the  signal  being  placed  at  danger  behind  a  train  the 
act  of  unlocking  the  signal  lever  opens  the  staff  circuit,  and  no  com- 
munication can  be  made  between  the  two  staff  stations  until  the  sig- 
nal is  at  danger,  and  the  lever  locked  in  that  position.  This  does  not 
indicate,  however,  that  the  operator  will  have  the  staff  ready  for  de- 
livery by  hand,  or  in  the  mechanical  deliverer.  To  cover  this  point 
an  electric  slot  is  attached  to  the  signal  governing  train  movements 
into  the  staff  section,  which  slot  is  controlled  by  the  staff  and  lever 

lock  and  the  mechani- 
cal deliverer,  so  that 
before  the  signal  can 
be  cleared  the  staff 
must  be  released,  used 
.to  unlock  the  signal 
lever  and  put  in  the 
staff  deliverer,  which 
closes  the  circuit  on 
the  electric  slot.  The 
signal  can  then  be 
cleared.  With  this  ar- 
rangement, therefore,  a 
clear  signal  can  not  be 
given  until  the  staff  is 
actually  in  the  deliv- 
erer. 

When  the  train  picks 
up  the  staff,  the  circuit 
on  the  slot  is  opened, 
automatically  setting 
the  signal  to  danger, 
which  can  not  again 
be  cleared  until  the  op- 
eration described  above 
is  repeated. 

SWITCH    LOCKING 

The  staff  is  also  used 
as  a  key  to  unlock  siding  switches  which  may  occur  between  staff 
stations,  the  switch  locks  being  so  designed  that  the  staff  cannot  be 
removed  from  the  lock  until  the  switch  is  set  and  locked  for  the 
main  line,  thus  providing  absolute  protection  against  misplaced 
switches. 


FIG.    4O — FRONT    VIEW  OF  STAFF  INSTRUMENT  WITH 
PERMISSIVE  AND  PUSHER  ATTACHMENTS 


RAILWAY  SIGNALING 


69 


SIDING  AND  JUNCTION  INSTRUMENTS 

In  some  sections  there  is  a  siding  of  sufficient  length  to  hold  a 
train,  but  traffic  would  not  warrant  placing  a 
staff  at  this  point.  That  the  usefulness  of  this 
long  siding  may  not 
be  lost,  a  special  in- 
strument is  placed 
at  the  siding  which 
enables  it  to  be  used 


FIG.    41  —  PERMISSIVE 


for  meeting  or  pass-   FIG.  42  —  PERMISSIVE  STAFF 
ing  trains.  ASSEMBLED 

The  operation  is  as  follows :  A  train  ar- 
riving at  the  staff  station  X  has  not  time  to 
proceed  to  Y,  but  can  proceed  as  far  as  the 
siding.  The  operator  at  X  gives  the  train  a 
staff  with  instructions  to  proceed  to  the  siding. 
Unlocking  the  switch  with  the  staff,  the  train 


sS^KSsjJ^D      takeS    thC    Sidin£'    ClOS6S    and    10CkS    thC    Switdl> 
DOOR   OPEN 


places  the  staff  in  the  siding  instrument,  and 


turns  the  drum  to  the  right. 


The  staff  is  now  locked  in  the  instru- 
._     ment,  and   the    staff   in- 
struments  at   X   and    Y 


FIG.  43  —  PARTS  OF  PERMISSIVE  STAFF 


are  synchronized,  and  the  fact  indicated  to  both 
operators  so  that  trains  may  be  sent  through 
the  section  in  either  direction.  FIG.  44  —  BACK  VIEW 

When  all  trains  having  precedence  over  the 


one  in  the  siding  have  passed  through  the  sec-     ING   MECHANISM 
tion,  and  the  staffs  have  been  replaced  in  the  instruments  ;  X  and  Y 


;o  RAILWAY  SIGNALING 

acting  in  conjunction  can  release  the  staff  at  the  siding,  which  on 
being  removed  changes  the  circuits  so  that  no  staff  can  be  released 
either  at  X  or  F.  The  train  on  the  siding  then  unlocks  the  switch 
with  the  staff  and  proceeds  to  F  or  back  to  X. 

A  junction  or  diverging  line  may  be  situated  between  two 
points  most  suitable  for  staff  stations ;  but  on  account  of  the  small 
amount  of  traffic  over  the  diverging  line  it  would  not  be  desirable  to 


FIG.    45 — VIEW    OF    STAFF   LEVER   LOCK    WITH    CASE    REMOVED 

make  it  a  staff  station.     Such  a  point  can  be  controlled  in  a  similar 
manner. 

PUSHER  ENGINE  ATTACHMENT 

Another  adjunct  to  the  staff  system  is  known  as  the  pusher  en- 
gine attachment  and  staff  (Fig.  40)  which  is  used  on  heavy  grades 
where  pusher  engines  are  required,  and  is  intended  to  both  obviate 
the  necessity  of  the  pusher  engine  proceeding  through  the  entire  staff 
section,  and  to  better  equalize  the  traffic.  It  can  readily  be  seen 
from  the  foregoing  description  of  the  staff  system  that  under  ordi- 
nary rules  every  train  having  a  pusher  engine  attached  would  receive 


RAILWAY  SIGNALING 


one  staff  to  proceed  up  grade  as  from  X  to  F.  On  arrival  at  F  the 
pusher  engine  would  necessarily  have  to  receive  a  staff  to  return  to 
X.  Supposing  the  traffic  up  and  down  grade  to  be  equal  and  that 
each  train  going  up  grade  requires  a  pusher,  it  is  apparent  that  twice 
as  many  staffs  would  go  down  hill  as  came  up,  resulting  eventually 
in  all  the  staffs  arriving  at  the  foot  of  the  grade,  X,  from  which  they 

could  only  be  returned  to  F  by 
some  special  person  authorized  to 
unlock  the  instruments  and  remove 
the  staffs  by  hand.  Furthermore, 
the  summit  of  the  grade  may  be 

FIG.  46-pusHER  STAFF  half-way  between  X  and  Y,  but  un- 

der the  rules  a  pusher  could  not  cut  off  at  the  summit  and  return  to 
F,  but  must  continue  on  to  X  and  receive  a  staff  to  return. 

To  overcome  these  two  objections  the  pusher  attachment  is  em- 
ployed. It  consists  (like  the  permissive  attachment)  of  a  separate 
device  which  may  be  attached  to  any  absolute  instrument  (Fig.  40) 
and  contains  a  staff  of  special  design  (Fig.  46)  which  can  only  be 
released  by  a  regular  staff,  though,  unlike  the 
permissive  staff,  it  can  be  out  of  its  receptacle 
at  the  same  time  as  the  regular  staff,  but  when 
so  removed  it  opens  the  controlling  circuits  of 
the  system,  preventing  any  other  movement  be- 
ing made  until  it  has  been  returned  and  locked 
in  the  pusher  attachment.  Fig.  47  is  a  rear 
view  of  a  pusher  atachment  showing  the 
mechanism. 

The  operation  is  as  follows :  A  train  with  a 
pusher  wishes  to  proceed  from  X  to  Y.  Y  re- 
leases a  staff  at  X,  and  X  uses  this  staff  to  re- 
lease the  pusher  staff.  X  then  hands  the  regu- 
lar staff  to  the  train  and  the  pusher  staff  to  the 
pusher  engineer.  The  train  passes  through 
the  section  and  delivers  the  regular  staff  at  Y. 
This  is  placed  in  the  instrument  there,  the 
pusher  engine  retaining  the  pusher  staff  and  returning  to  X.  Until 
this  latter  staff  is  put  into  the  pusher  attachment  at  X  and  locked, 
the  staff  circuits  are  not  re-established  and  no  other  staff  can  be  re- 
leased. 


FIG.  47  —  BACK  VIEW 
OF  PUSHER  ATTACH- 
MENT SHOWING 
MECHANISM 


CHAPTER  V 

AUTOMATIC  BLOCK  SIGNALING 
GENERAL 

GIVEN  a  section  of  railroad  from  which  large  earnings  are  to 
be  derived  and  assuming  that  there  is  plenty  of  business 
to  handle,  the  problem  is  to  move  the  maximum  number  of 
trains  over  it  with  economy  and  safety.     If  every  train  had  a  track 
of  its  own,  no  block  system  would  be  necessary,  but  on  the  leading 
railroad   systems   the  traffic   has   increased   much   faster   than   the 
trackage.     One  of  the  most  helpful  and  efficient  means  for  safely 
handling  a  large  number  of  trains  over  the  same  track  is  a  good 
block  system. 

DEFINITIONS   AND   CLASSIFICATIONS 

Before  enlarging  upon  this  subject,  a  few  definitions  may  be  of 
value  to  the  reader. 

A  block  is  a  length  of  track  of  defined  limits,  the  use  of  which 
by  trains  is  controlled  by  fixed  signals. 

A  block  signal  is  a  fixed  signal  controlling  the  use  of  a  block. 
The  word  "fixed"  refers  to  location  only  since  block  signals  are 
movable  signals  in  fixed  locations. 

Block  signals  may  be  classified  in  three  ways : 

ist — As  to  the  manner  in  which  their  day  indications  are  dis- 
played. 

2d — As  to  the  manner  in  which  they  are  controlled  and  op- 
erated. 

3d — As  to  what  they  control. 

Under  the  first  classification  there  are : 

(a)  Banner  signals,  the  indications  being  displayed  by  a  re- 
volving banner. 

(b)  Disc  signals,  the  indications  being  displayed  by  a  movable 
disc  in  front  of  a  fixed  background;  and 

(c)  Semaphore  signals,  the  indications  being  displayed  by  the 
position  of  an  arm  moving  in  a  plane  at  right  angles  to  the  track. 
In  all  types  under  class  one  the  night  indications  are  displayed  by 
tolored  lights. 

Under  the  second  classification  there  are : 

(a)   Manual,  the  signal  being  controlled  and  operated  by  man 


RAILWAY  SIGNALING  73 

power,  (b)  Controlled  manual,  the  signal  being  operated  manually 
and  constructed  so  as  to  require  the  co-operation  of  the  signalmen 
at  both  ends  of  the  block,  (c)  Automatic,  the  signal  being  operated 
by  power  which  is  controlled  entirely  by  the  presence  or  absence  of 
a  train  in  the  block,  or  the  condition  of  the  track. 
Under  the  third  classification  there  are : 

(a)  Home  block  signal,  a  fixed  signal  at  the  entrance  of  a  block 
to   control   trains   in   entering  and  using  said  block.      The   indica- 
tions displayed  by  a  home  signal  are  "stop"  and  "proceed",  or  in 
some  cases  "stop",  "caution"  and  "proceed". 

(b)  Distant  block  signal,  a  fixed  signal  used  in  connection  with 
a  home  block  signal  to  regulate  the  approach  thereto. 

An  absolute  block  system  is  one  which  never  allows  more  than 
one  train  in  the  same  block  at  the  same  time. 

A  permissive  block  system  is  one  which  may  allow  more  than 
one  train  in  the  same  block  at  the  same  time,  provided  the  trains  are 
going  the  same  direction  and  the  second  train  has  been  warned  by 
signal  that  another  train  is  in  the  block. 

EARLY  BLOCK  SYSTEMS 

The  older  block  systems  in  this  country  were  all  manual  or 
manually  controlled,  following  the  practice  in  England  and  Germany. 
The  enormous  increases  in  the  amount  of  traffic  to  be  handled  with 
only  slight  increases  in  trackage,  together  with  the  fallibility  of 
the  signalmen  operating  the  signals,  led  to  the  development  and  use 
of  automatic  block  signals.  Briefly,  both  economy  and  safety  led 
to  this  development.  In  the  days  when  the  station  agent  was  ticket 
agent,  baggage  man,  freight  agent,  freight  handler,  telegraph  opera- 
tor, etc.,  it  was  thought  that  to  let  him  also  handle  the  manual  block 
signals  would  be  good  for  him  while  he  was  resting.  As  traffic  in- 
creased, these  various  duties  became  more  and  more  onerous,  the 
stations  were  not  close  enough  together  to  be  serviceable  as  block 
stations,  and  the  men  became  too  busy  to  handle  the  signals  reliably. 

The  next  move  was  to  install  block  stations  in  the  outlying  dis- 
tricts. This  meant  a  first  cost  of  about  $i  ooo  for  the  station  and 
signals,  and  a  yearly  wage  cost  of  not  less  than  $i  ooo  to  $i  500  for 
each  block  station.  Furthermore,  the  men  still  made  mistakes  and 
gave  wrong  signals. 

AUTOMATIC   BLOCK   SIGNALS 

The  automatic  block  signal  must  be  a  permissive  signal  in  order 
that,  if  a  signal  is  out  of  order  and  assumes  the  stop  position,  traffic 


74  RAILWAY  SIGNALING 

may  not  be  entirely  suspended  for  several  hours.  On  double  track 
lines  this  is  not  serious,  as  a  train,  after  stopping  at  a  signal  out  of 
order,  may.  proceed  with  caution  through  the  block  expecting  thai 
another  train  is  already  ahead  of  it  in  the  block,  that  a  switch  is 
misplaced  or  that  a  rail  is  broken.  On  single  track  lines  it  was 
thought  that  the  delays  might  become  serious,  since  when  a  train  re- 
ceives a  stop  signal  it  is  necessary  to  protect  it  by  sending  a  flagman 
ahead  through  the  block.  For  this  reason  automatic  blocking  on 
single  track  has  not  met  with*  general  favor.  The  only  two  single 
track  lines  using  this  system  extensively  are  the  C.  N.  O.  &  T.  P. 
Ry.  and  the  Harriman  Lines,  the  latter  having  installed  several 
thousand  automatic  signals  on  single  track.  The  Harriman  Lines 
already  claim  to  have  shown  that  the  expense  of  the  system  was 
warranted  on  account  of  the  numerous  cases  of  broken  rails  which 
have  been  reported  by  the  automatic  signals. 

It  is  the  purpose  of  this  article  to  describe  only  the  arrange- 
ments of  signals  in  common  use  on  double  track  lines  and  the  auto- 
matic electric  semaphore  signal  which  is  in  most  general  use. 

LENGTH  OF  BLOCKS 

The  ideal  arrangement  of  automatic  signals  to  secure  the  max- 
imum capacity  for  train  movements  over  a  given  piece  of  track 
would  be  to  first  decide  upon  the  maximum  distance  required  for 
stopping  any  train  on  the  road.  This  can  be  decided  from  the  air 
brake  tests,  and  this  distance  would  have  to  be  the  minimum  length 
of  the  block.  Since  it  is  more  difficult  to  stop  on  a  descending  grade 
and  less  difficult  to  stop  on  an  ascending  grade,  the  blocks  would 
gradually  be  lengthened  out  on  the  descending  grade  and  gradually 
shortened  on  ascending  grades.  As  large  terminals  are  approached 
the  blocks  would  gradually  be  shortened  on  account  of  the  limited 
speed  of  trains  and  congestion  of  traffic  at  such  places.  Having 
fixed  the  locations,  the  control  of  the  signals  should  be  such  as  not 
only  to  warn  an  engineman  when  he  reaches  a  block  which  is  oc- 
cupied, but  also  to  warn  him  in  time  to  permit  him  to  stop  his  train 
before  reaching  the  entrance  of  the  occupied  block.  With  this  ar- 
rangement and  control  of  signals  it  would  be  possible  to  start  two 
trains  from  one  end  of  the  line  two  blocks  apart,  run  them  the  length 
of  the  road  at  the  same  speed  and  have  them  arrive  at  the  other  end 
still  just  two  blocks  apart.  The  second  train  would  receive  clear 
signals  all  the  way;  or  if  the  first  train  should  stop  at  any  point,  the 
second  would  receive  due  warning  and  would  have  plenty  of  space 


RAILWAY  SIGNALING  75 

to  stop  in  before  reaching  the  block  which  was  occupied  by  the  first 
train. 

In  ordinary  practice  to-day  the  minimum  length  of  block  is 
seldom  used,  and  the  length  commonly  varies  from  4  ooo  feet  to 
12  ooo  feet.  Frequently  so  little  heed  is  paid  to  the  principles  men- 
tioned above  that  the  ideal  arrangement  is  far  from  being  reached. 
One  of  the  principal  reasons  for  improper  spacing  is  that  if  a  signal 
is  located  in  its  proper  place  for  uniform  spacing  of  trains,  it  cannot 
be  readily  seen  on  account  of  the  curvature  of  the  line  or  obstruc- 
tions to  the  view,  such  as  bridges.  All  of  the  diagrams  of  signal 
arrangement  in  Figs.  48  to  52  show  the  home  signals  as  arms  with 
square  ends  and  the  distant  signals  as  arms  with  forked  ends.  In 
every  case  the  block  is  the  space  between  home  signals,  the  distant 
signals  being  nothing  more  than  repeaters  for  the  home  signals. 

SEMAPHORES  ON   SEPARATE  POSTS 

Fig.  48  illustrates  the  arrangement  of  signals  in  an  automatic 
block  system  using  semaphore  home  and  distant  signals  mounted  on 


FIG.    48 

separate  posts.  This  arrangement  is  used  very  little  excepting  where 
traffic  is  light  and  the  home  block  signals  are  considerably  more  than 
one  mile  apart.  The  distant  signals  would  probably  be  located  not 
more  than  4  ooo  feet  from  their  respective  home  signals. 

A  home  signal  is  shown  at  a  in  the  stop  position  with  a  train 
just  past  it  in  the  block.  The  arm  is  horizontal  and  a  red  light 
would  be  displayed  at  night.  It  means  "stop  and  wait  the  prescribed 
time  (usually  I  minute)  then  proceed  under  control  expecting  to 
find  a  train  in  the  block,  a  misplaced  switch  or  a  broken  rail."  The 
distant  signal  for  a  is  shown  at  at  and  is  in  the  "caution"  position. 
Some  roads  use  a  green  light  for  the  night  indication ;  others  use  a 
yellow  light  instead.  It  means  "expect  to  find  next  home  signal  in 
the  stop  position."  &  is  a  home  signal  in  the  proceed  position. 
The  arm  is  inclined  at  an  angle  of  60  or  75  degrees  from  the  hori- 
zontal. On  roads  using  green  for  "caution"  a  white  light  would  bt, 
displayed  at  night.  On  roads  using  yellow  for  "caution"  a  green 
light  would  be  displayed  at  night.  It  means  "proceed,  the  block  is 
unoccupied,  all  switches  are  set  right  and  rails  are  unbroken."  &t 


76  RAILWAY  SIGNALING 

is  the  distant  signal  for  b  and  is  in  the  proceed  position.  On  roads- 
using  green  for  "caution"  a  white  light  would  be  displayed  at  night. 
On  roads  using  yellow  for  "caution"  a  green  light  would  be  display- 
ed at  night.  It  means  "proceed,  expect  to  find  the  next  home  signal 
in  the  proceed  position." 

Using  this  arrangement,  trains  can  run  at  speed  if  spaced  a  dis- 
tance equal  to  one  block  (a  to  b)  plus  the  distance  between  a  home 

<*-  It  !£..  it 

=g=pr  :  a<g=G  z 

FIG.   49 

signal  and  its  distant  (b  to  b^)  or  ordinarily  about  10000  feet  -{- 
4000  feet  =  14000  feet  apart. 

On  most  roads  the  blocks  do  not  often  exceed  7  500  feet  ir 
length  and  it  has  been  found  convenient  as  well  as  economical  to 
use  the  arrangement  shown  in  Fig.  49,  which  shows  home  and  dis- 
tant signals  mounted  on  the  same  post. 

SEMAPHORES   ON    SAME   POST 

The  indications  and  meanings  of  the  signals  shown  in  Fig.  49 
are  identical  with  those  described  in  Fig.  48.  It  is  developed  by 
shortening  the  length  of  blocks  a  b  in  Fig.  48  until  av  and  b  are  so 
close  together  that  it  is  best  to  mount  them  on  the  same  post.  With 


FIG.  50 

this  arrangement  trains  running  at  speed  would  be  spaced  two 
blocks  apart,  although  the  actual  distance  might  be  the  same  or  less 
than  that  shown  in  Fig.  48. 

THREE    POSITION    SIGNALS 

Fig.  50  illustrates  the  arrangement  and  use  of  three  position  sig- 
nals. Each  signal  is  a  hcme  signal  and  distant  signal  combined,  a  is 
a  home  signal  in  the  "stop"  position.  The  arm  is  horizontal.  The 
meaning  is  the  same  as  a  in  Fig.  49.  The  night  indication  is  the  same 
as  a  in  Fig.  48.  b  is  a  home  signal  in  the  "caution"  position.  The 
arm  is  inclined  at  an  angle  of  45  degrees  from  the  horizontal.  The 
meaning  is  the  same  as  ba±  in  Fig.  49.  The  night  indication  is  the 
same  as  a^,  Fig.  48.  c  is  a  home  signal  in  the  "proceed"  position. 
The  arm  is  inclined  at  an  angle  of  90  degrees  from  the  horizontal. 


RAILWAY  SIGNALING  77 

The  meaning  is  the  same  as  cb^  Fig.  49.     The  night  indication  is 
the  same  as  b,  Fig.  48. 

The  semaphore  signal  is  primarily  a  position  signal,  yet  in  Figs. 
48  and  49,  both  arms  a  and  a^  are  in  the  horizontal  position  but  have 
two  entirely  different  meanings.  The  signals  shown  in  Fig.  50  are 


FIG.    51 

theoretically  more  correct  in  this  respect.  Both  schemes  are  exten- 
sively used,  both  have  arguments  in  their  favor,  and  both  have  many 
ardent  advocates.  As  far  as  the  spacing  of  trains  is  concerned, 
Figs.  48  and  49  are  exact  equivalents. 

OVERLAP    SYSTEMS 

Partial  block  length — An  "overlap"  system,  as  shown  in  Fig. 
51,  is  one  in  which  each  home  block  signal  is  so  controlled  that  it  will 
remain  in  the  stop  position  until  the  train  has  passed  a  certain  pre- 
scribed point  in  advance  of  the  next  home  signal.  It  has  been  used 
in  arrangements  like  Fig.  48,  but  presupposes  that  conditions  may 
arise  which  may  cause  an  engineman  to  run  by  a  home  signal  in  the 
stop  position  without  making  the  stop  and  gives  him  additional  space 
to  stop  in.  It  is  very  questionable  as  to  whether  it  should  be  used 
except  in  unusual  cases  where  the  blocks  are,  on  account  of  traffic, 

d  c, 

UL, 


FIG.   52 

very  short  and  it  is  doubtful  as  to  whether  a  train  can  stop  in  the 
length  of  one  block  only.  This  system  is  open  to  the  objection  that, 
if  an  engineman  knows  that  there  are  at  times  two  stop  signals  be- 
tween him  and  the  preceding  train,  he  may  assume  that  there  are 
always  two  stop  signals  between  and  run  by  the  first  without  at- 
tempting to  stop. 

If,  as  in  some  of  the  earliest  installations,  home  signals  only 
are  used,  the  overlap  is  necessary  because  in  many  cases  local  con- 
ditions will  not  permit  the  location  of  signals  so  that  they  are  visible 
a  safe  stopping  distance  away.  The  distant  signal  takes  the  place 
of  the  overlap  except  where  the  blocks  are  extremely  short.  With 
the  arrangement  shown  in  Fig.  51,  trains  would  be  spaced  two  and 
one-half  blocks  apart. 


78  RAILWAY  SIGNALING 

Full  block  length — Another  overlap  system  is  shown  in  Fig. 
52  which  differs  from  Fig.  51  in  that  the  overlap  is  a  full  block  in 
length.  With  this  arrangement  trains  would  be  spaced  three  blocks 
apart.  This  system  is  used  in  the  New  York  Subway.  There  the 
blocks  are  only  800  feet  long  and  there  is  a  full  block  overlap  and 
each  signal  has  an  automatic  train  stop  working  in  conjunction 
with  it. 

In  the  foregoing  description  the  spacing  of  trains  refers  to  their 
spacing  if  they  are  running  at  speed  past  all  signals  in  the  proceed 
position.  In  Figs.  48  to  51  the  second  train  would  not  have  to  actu- 
ally stop  until  it  reached  the  signal  a.  In  Fig.  52  the  second  train 
would  not  have  to  stop  until  it  reached  the  signal  b. 

CONSTRUCTION 

Counterweights — All  automatic  signals  must  be  so  constructed 
that  the  weight  of  all  moving  parts  tends  to  restore  the  signal  to  the 
stop  position.  To  secure  this  with  all  of  the  signals  illustrated  the 
semaphore  arm  has  to  be  counterweighted.  The  counterweight 
must  be  sufficient  to  carry  the  arm  to  "stop"  even  when  it  is  cover- 
ed with  snow  and  ice. 

It  is  plain  that,  if  the  arm  traveled  in  a  quadrant  above  the  hor- 
izontal, little  counterweight  would  be  necessary  and  the  arrangement 
would  be  safer  and  more  economical  of  power.  Recently  signals 
having  arms  working  in  the  upper  quadrant  have  been  installed  on 
the  Pennsylvania  railroad  and  the  scheme  is  being  urged  on  many 
other  roads.  In  such  an  arrangement  the  meanings  of  the  signals 
would  correspond  with  the  meanings  of  arms  at  equal  angles  in  the 
lower  quadrant. 

If  an  automatic  signal  is  so  counterweighted  that  it  will  go  to 
the  "stop"  position  by  the  force  of  gravity,  it  is  evident  that  it  must 
be  moved  to  the  "proceed"  position  by  the  application  of  power  and 
held  there  by  power.  Before  going  into  the  construction  of  the 
signals  themselves  it  is  well  to  see  how  a  train  in  passing  a  signal 
in  the  proceed  position  cuts  off  the  power  so  that  gravity  returns 
it  to  the  "stop"  position. 

The  track  circuit — The  track  circuit  is  the  foundation  of  every 
automatic  block  system.  It  is  its  main  element  of  strength  and  it  is 
also  one  of  its  weakest  elements  if  we  are  to  consider  the  many  an- 
noying troubles  which  arise  from  it.  The  track  circuit  was  invented 
in  1872  and  has  been  used  in  all  kinds  of  signaling  and  protective 
schemes.  The  installation  of  a  section  of  track  circuit  is  very  sim- 


RAILWAY  SIGNALING  79 

pie.  It  merely  means  the  removal  of  one  of  the  iron  fish  plate  joints 
from  each  rail  at  each  end  of  the  section  and  replacing  them  with 
one  of  the  many  types  of  insulated  joints;  the  bonding  together  of 
the  intermediate  rails  by  running  bonds  of  No.  8  galvanized  iron 
wire  around  each  joint  and  connecting  a  battery  across  the  rails  at 
one  end  and  an  electro-magnet  across  the  rails  at  the  other  end. 
From  the  diagram  in  Fig.  33-  it  may  be  seen  that  this  would  form  a 
closed  circuit,  the  rails  simply  connecting  the  battery  to  the  electro- 
magnet. This  electro-magnet  is  called  a  relay.  It  has  a  pivoted 
armature  weighted  so  that  it  will  fall  away  from  the  cores  by  grav- 
ity and  the  magnet  must  be  energized  to  raise  it.  The  moving  arm- 
ature  carries  moving  contacts  for  controlling  auxiliary  electric  cir 
cuits  and  is  used  to  control  the  operating  circuit  for  a  signal.  The 
wheels  of  the  train  when  on  the  track  circuit  offer  so  little  resist- 
ance to  the  current  that  the  relay  does  not  get  enough  current  to 


Insukted  Insulated 


Rails 


Relay 


FIG.   53 

hold  the  armature  up.  It  then  falls  and  opens  the  signal  operating 
circuit. 

While  the  track  circuit  is  fundamentally  very  simple  it  has  been 
very  difficult  to  make  the  arrangement  operate  under  all  conditions 
for  the  following  reasons : 

ist — There  is  no  insulation  between  rails  except  the  ties  and 
ballast  and  during  wet  weather  the  leakage  between  rails  is  consid- 
erable. 

2nd — The  source  of  current  is  usually  a  gravity  battery,  al- 
though in  recent  installations  some  storage  batteries  are  used.  The 
voltage  and  current  capacity  in  the  case  of  the  gravity  battery  are 
low  and  the  problem  is  to  arrange  the  cells  so  as  to  furnish  enough 
current  to  feed  the  leakage  between  rails  and  also  feed  the  relay 
enough  current  to  operate  it  satisfactorily  in  wet  weather. 

The  actual  figures  in  regard  to  the  amount  of  power  used  to 
operate  one  track  circuit  seem  ridiculously  small  to  an  electrical  en- 
gineer. For  instance,  the  total  amount  of  energy  expended  for  one 


8o  RAILWAY  SIGNALING 

track  section  is  seldom  more  than  one-half  of  a  watt.  The  amount 
needed  to  operate  the  relay  is  less  than  one-fourth  of  a  watt.  Yet  it 
is  a  difficul  task  to  hang  on  to  that  one-half  watt  through  from  2  ooo 
to  5  ooo  feet  of  track  with  low  insulation  between  rails. 

The  voltage  used  is  ordinarily  from  one  to  two  volts.  If  the 
voltage  is  increased  much  above  this  the  leakage  is  so  excessive  that 
the  gain  at  the  relays  is  very  little.  If  the  resistance  of  the  relay  is 
much  above  nine  ohms  the  relay  will  not  work  in  wet  weather.  If 
the  resistance  is  much  below  four  ohms  the  train  will  not  cause  it  to 
open. 

The  energy  expended  is  divided  in  some  such  way  as  this : 

Ten  percent  is  used  to  overcome  resistance  of  rails  and  connec- 
tions to  battery  and  relay. 

Fifty  percent  is  lost  by  leakage. 

Forty  percent  is  used  in  operating  the  relay. 

3rd — The  relay  must  be  inclosed  and  sealed  so  that  careless 
maintainers  cannot  adjust  or  tamper  with  it,  and  moisture  cannot 
get  on  the  contacts  moved  by  the  armature  and  freeze  them  closed. 
It  must  be  protected  by  high  grade  insulation  in  all  its  parts  so  that 
lightning  cannot  fuse  its  contacts,  and  must  also  be  protected  by  a 
first  class  lightning  arrester. 


CHAPTER  VI 

AUTOMATIC  BLOCK  SIGNALING 
DIRECT    CURRENT 

IN  GENERAL,  all  signal  circuits  should  be  so  arranged  that  a 
closed  circuit  is  employed  to  give  all  safety  indications  and  the 
operating  battery  should  be  at  the  end  of  the  circuit  farthest 
from  the  apparatus,  in  order  that  any  crossed  wires,  broken  wires  or 
loss  of  power  will  cause  a  danger  indication. 

The  simplest  system  of  circuits  is  the  polarized  track  circuit 
system  shown  in  Figs.  4^ and  $£.  Fig.  ^-illustrates  the  application  of 
the  polarized  system  to  an  arrangement  of  signals  where  the  home 
and  distant  arms  are  mounted  on  the  same  post.  H '  shows  the  wir- 
ing at  the  last  signal  of  the  system  which  would  have  no  signal  in 
advance  and  consequently  no  distant  arm. 

The  home  arm  at  this  point  is  controlled  through  the  contact  of 
a  neutral  relay,  R,  connected  to  the  track  section  in  advance  of  it. 
The  battery  for  the  track  section  in  the  rear,  instead  of  being  con- 
nected direct  to  the  rails,  is  carried  through  a  pole  changing  circuit 
controller  which  is  operated  by  the  signal  arm.  With  the  arm  in  the 
stop  position  the  pole  changer  would  shift  the  battery  from  AD-BC, 
as  shown  in  heavy  lines,  to  AC-BD  as  shown  in  dotted  lines,  thus 
reversing  the  polarity  of  the  battery  as  applied  to  the  rails.  H 
shows  the  wiring  at  all  other  signal  locations.  The  home  arm  is 
controlled  through  contact  K  of  relay  R,  the  same  as  the  home  arm 
at  H!  Contact  K  is  called  the  neutral  contact  and  is  open  or  closed 
depending  upon  the  amount  of  current  flowing  through  the  electro- 
magnet coils,  and  not  by  its  polarity. 

Contact  K '  is  operated  from  another  armature  on  the  same  re- 
lay. This  armature  is  a  permanent  magnet  which  swings  to  either 
pole  of  the  electro-magnet  of  the  relay  and  thus  shifts  the  contact 
K '  whenever  the  polarity  of  the  electro-magnet  changes. 

The  distant  arm  is  controlled  through  both  K  and  K '  so  that 
the  distant  operating  circuit  will  be  closed  whenever  the  home  arm 
in  advance  has  been  cleared  and  the  battery  on  the  track  is  of  the 
polarity  shown.  The  distant  arm  is  also  controlled  through  a  circuit 
controller  operated  by  the  home  arm  on  the  same  post.p" — 

Fig.  ojGj  shows  the  same  scheme  applied  to  an  arrangement  of  sig- 
nals where  the  home  and  distant  arms  are  mounted  on  separate  posts. 

Kig.V56  >sjiowfi.  a  sectional^ie^  cHr a  Central  type^of  relay. 


RAILWAY  SIGNALING 


Fig.  ^  show^-a  sectional  view  of  ^a  cofnbine^i-rieutral^atitf  pol^br- 
ized  type  of  relay,, 

If  it  is  assumed  that  there  is  a  train  in  the  section  in  advance  of 
H'  the  home  arm  at  H  '  would  be  in  the  "stop"  position  and  the  bat- 
tery would  be  reversed  on  the  track  section  HH! 

At  H  the  contact  K  would  be  closed  and  the  contact  K  ' 
would  be  open  so  that  the  home  arm  would  be  in  the  "proceed"  posi- 


FIG.  54 

tion  and  the  distant  arm  would  be  in  the  "caution"  position.  When 
the  train  passes  out  of  the  section  and  the  home  arm  at  H '  goes  to 
the  proceed  position,  thus  reversing  the  polarity  of  the  battery  on  the 
track  section  HH',  it  may  be  noted  that  while  the  pole  changer  is 
shifting,  i.  e.,  for  a  fraction  of  a  second,  the  relay  at  H  would  be  de- 
energized  arid  the  contact  K  would  open  and  then  close.  This  open- 
ing of  contact  K  would  tend  to  release  the  home  arm  at  H  and  re- 
turn it  to  the  "stop"  position  if  provisions  were  not  made  to  prevent 


FIG.  55 

it.  This  is  prevented  by  applying  a  closed  circuit  inductive  coil  to 
the  relay  R  or  to  the  holding  magnet  of  the  signal,  either  of  which 
will  hold  the  signal  arm  clear  momentarily  by  induction.  If  this 
slow  releasing  feature  is  applied  to  the  relay,  the  contact  K  will  re- 
main closed  long  enough  for  the  pole  changer  to  shift.  If  it  is  ap- 


RAILWAY  SIGNALING  83 

plied  to  the  holding  magnet  of  the  signal  it  will  hold  the  arm  long 
enough  for  the  pole  changer  to  shift  in  spite  of  the  fact  that  K  may 
open  for  an  instant.  The  latter  scheme  is  usually  employed.]  ^X)  * 
Another  automatic  block  signal  system  which  is  if  anything  bet- 
ter suited  to  meet  all  around  conditions  than  the  polarized  system 
provides  for  the  control  of  distant  signals  by  line  wires  as  shown  in 
Fig.  £@.  The  home  ;irms  are  controlled  directly  from  the.  track  re- 
lays as  previously  described  but  the  distant  arm  a1  is  controlled 
through  an  additional  relay  R2  which  in  turn  is  controlled  through 
line  wires  and  a  circuit  controller  (c)  operated  from  the  home  arm 
a  in  advance.  The  distant  arm  is  also  controlled  by  a  circuit  con- 
troller operated  by  the  home  arm  b  on  the  same  post.  The  line 


FIG.  56 — SECTIONAL  VIEW  OF  NEUTRAL 
TYPE    RELAY 


FIG.  57 — SECTIONAL  VIEW  OF  COMBINED 
NEUTRAL  AND  POLARIZED  TYPE  RELAY 


wires  have  to  be  protected  with  lightning  arresters  but  even  then  the 
distant  arms  are  frequently  out  of  service  on  account  of  lightning. 
For  this  reason  other  schemes  which  provide  for  the  control  of  the 
home  arms  through  line  wires  are  objectionable  and  cause  unneces- 
sary delays  to  traffic. 

Fig.  sl-also  shows  what  is  done  when  the  track  section  between 
signals  is  too  long  to  operate  as  one  section.     It  may  be  noted  that 
the  track  circuit  is  relayed  at  the  cut  sections  by  a  method  somewhat 
similar  to  that  employed  in  telegraph  lines.     Usually^from  3  ooo  ^W 
5  ooo  feet  of  track  can  be  operated  without  a  cut.  ^ThTsignal  oper> 
ating  batteries  B  and  B '  each  consist  of  16  cells  of  caustic  potash 


84 


RAILWAY  SIGNALING 


primary  battery,  connected  in  series  and  housed  in  a  receptacle 
placed  sufficiently  deep  to  prevent  freezing ;  or  they  might  each  con- 
sist of  five  cells  of  storage  battery  in  an  iron  cas'e  beneath  the  signal 
operating  mechanism.  The  track  batteries  B2-B&  consist  of  two  or 
three  cells  of  gravity  battery  connected  in  multiple  and  placed  in  an 
iron  chute  below  the  frost  level.  One  cell  of  storage  battery  with 
from  one  to  two  ohms  resistance  in  series  with  it  may  be  used  in- 
stead. Fig.  59  shows  a  cut  section  of  a  typical  battery  and  relay 
shelter.  Storage  batteries  give  the  best  results  on  both  track  and 
signal  operating  circuits,  but  their  first  cost  is  usually  greater. 

Fig.  60  shews  the  signal  operating  mechanism  now  almost  ex- 
clusively used  on  the  leading  railroads.  About  25  ooo  are  in  use. 
It  consists  primarily  of  a  motor  and  an  electric  clutch  or  holding 


HM 

Bi 


Line  wires 


FIG.    58 — DIAGRAM   OF  CONNECTIONS   WHEN  TRACK  CIRCUIT  RELAY  IS   USED 

magnet,  the  latter  being  mounted  on  a  compound  lever  to  which  the 
operating  rod  of  the  signal  arm  is  attached  near  the  center.  This 
compound  lever  is  pivoted  near  one  end  and  the  motor,  through  a 
train  of  gears,  drives  a  chain  carrying  a  trunion  which  engages  with 
the  free  end  of  the  lever  and  raises  it  when  the  operating  current  is 
applied  to  the  motor  and  magnet.  After  the  arm  is  raised  the  motor 
is  automatically  cut  out  and  stopped  by  a  friction  brake.  The  end 
of  the  lever  then  drops  back  a  little  and  rests  on  a  catch  where  it  is 
held,  free  from  the  motor  gearing  and  chain,  until  the  magnet  is  de- 
energized  by  the  opening  of  the  control  relay.  When  the  magnet  is 
de-energized  the  lever  arm  drops  down  by  gravity  because  the  arma- 
ture of  the  magnet  releases  the  train  of  levers  in  the  arm  and  thus 
releases  the  end  of  the  arm  from  the  catch.  The  fall  of  the  lever 
arm  is  eased  by  means  of  the  dash-pot  connected  outside  the  pivot 
end. 

Fig.  60  shows  a  two  arm  movement,  the  lever  arm  at  the  front 


RAILWAY  SIGNALING 


being  lifted  to  operate  the  home  signal  arm  and  the  lever  arm  at  the 
back  being  down  with  the  distant  signal  arm  in  the  "caution"  posi- 
tion. '-Beneath  the  clutch,  or  slot 
magnet,  as  it  is  called,  is  the  pole 
changer  operated  by  the  home 
signal  lever  arm.  ^ 

The  leverage  is  such  that  the 
armature  of  the  slot  magnet  has 
to  hold  up  only  from  one  to  three 
pounds,  although  the  combined 
load  of  operating  rod,  signal  arm 
and  slot  lever  arm  is  over  100 
pounds.  The  slot  magnets  are 
compound  wound,  a  low  resist- 
ance winding  being  in  series  with 
the  motor  and  cut  out  with  it, 
and  a  high  resistance  winding 
(500  to  2  ooo  ohms)  being  in 
multiple  with  the  motor  to  hold 
the  arm  after  the  motor  cuts  out. 
The  operating  voltage  is  usual- 
ly about  ten  volts,  the  time  re- 
quired for  operating  one  arm 
about  six  seconds,  and  the  motor 
current  about  two  amperes. 

This  mechanism  is  exception- 
ally free  from  friction,  the  arma- 
ture of  the  slot  magnet  is  far 
enough  from  the  core  so  that  it 
cannot  be  held  by  residual  mag- 
netism and  the  weight  of  all 
moving  parts  tends  to  restore  the 
signal  to  the  stop  position  as  soon 
as  the  track  relay  cuts  off  the 
battery  current. 

The  protection  of  switches  in 
block  signal  territory  has  been 
left  to  the  last  in  order  that  the 
main  scheme  might  not  be  confus- 
ing. Each  switch  is  insulated  so  that  the  track  circuit  passes  through 
it  unbroken.  A  circuit  controller  such  as  shown  in  Figs.  61  and  62  is 


FIG.    59 — SECTIONAL    VIEW    OF    BATTERY 
AND    RELAY    SHELTER 


86 


RAILWAY  SIGNALING 


attached  to  the  point  of  the  switch  and  adjusted  so  that  if  the  switch 
is  open  one-fourth  of  an  inch  the  track  circuit  will  be  short-circuited 
as  if  by  the  presence  of  a  train.  For  the  guidance  of  trains  com- 
ing  out  of  a  siding  onto  the  signaled  track,  a  switch  indicator 
mounted  on  an  iron  post  near  the  switch  is  employed.  The  switch 
indicator  is  usually  so  controlled  that  when  a  train  is  approaching 


FIG.   60 — ELECTRIC  SIGNAL  OPERATING   MECHANISM 

The  right  hand  rod  at  the  top  connects  with  the  home  signal 
arm  and  the  left  hand  rod  connects  with  the  distant  signal  arm. 
There  is  a  second  chain  back  of  the  one  shown  for  operating  the 
distant  lever  arm. 

on  the  main  track  two  blocks  away  the  miniature  semaphore  is  set  to 
the  "stop"  position  to  warn  the  train  in  the  siding  not  to  open  the 
switch.  All  sidings  are  made  a  part  of  the  track  circuit  up  to  the 


RAILWAY  SIGNALING  87 

fouling  point  to  protect  trains  on  the  main  track  from  cars  which 
may  not  clear  it. 

The  average  cost  for  an  automatic  block  system  using  home 
and  distant  signals  on  the  same  post  is  from  $750  to  $1100  per 
block  section,  depending  on  the  length  of  block,  number  of  switches 


FIGS.   6l    AND  62 — VIEW   OF   CIRCUIT   CONTROLLER  APPLIED   TO    SWITCH    AND 
ALSO  IN  DETAIL 

and  method  of  signal  control.  The  average  cost  of  maintenance 
and  operation  of  such  a  system  is  from  $75  to  $100  per  two-arm 
signal  per  year. 


CHAPTER  VII 

AUTOMATIC  BLOCK  SIGNALING— ALTERNATING-CURRENT 
GENERAL 

THE  proper  operation  of  a  direct-current  track  circuit  may  be 
interfered  with  when  the  track  rails  have  the  additional  duty 
of  conducting  current  for  other  purposes,  such  as  the  propul- 
sion of  trains.     It  has,  therefore,  become  necessary  to  use  a  kind  of 
signaling  current  in  the  rails  which,  while  performing  the  functions 
previously   described,  will  in  addition  be  able  to   operate  a  track 
relay  selectively;  i.e.,  which  will  respond  to  the  signaling  current 

Trolley  or  Third  Rail 


Car 


Propulsion     ^XT 
D.C  Generator  (°) 


Return  Rail 


Block  Rail 


Signal        // 
Signal  Light  4*0 


Rail  Insuktion 


1 

n         r 

i 

A. 

4  — 

Reactance  Coil 


AAAAA! 

N/WWI 


Track  Transformer 


Signal  A.  C.  Generator 


A.  C.  Signal  Mains 


FIG.    63 — TYPICAL    ALTERNATING-CURRENT   TRACK    CIRCUIT    USING    THE    SINGLE- 
RAIL   SCHEME 

and  to  no  other.     Thus  alternating  current,  because  of  its  inductive 
properties,  has  been  substituted  for  direct  current. 

Two  schemes  of  alternating  current  are  in  use,  the  single-rail 
return  system  and  the  double-rail  return  system.  In  the  former, 
one  rail  of  each  track  is  insulated  into  block  sections  for  signaling 


RAILWA Y  SIGNALING 


89. 


purposes,  the  other  rail  serving  as  a  continuous  return  for  the 
power  current  and  as  one  side  of  the  alternating-current  track  cir- 
cuit. In  the  latter,  both  are  insulated  into  block  sections  and  both 
are  used  for  the  power  current.  This  is  accomplished  by  the  use  of 

balanced  inductive  bonds  and  is  used  in 
preference  tx>  the  single-rail  system ,  un- 
der certain  conditions.  The  single-rail 
scheme  and  some  features  of  interest  in 
its  application  will  be  considered  in  this 
article. 


FIG.  64 — FORM  OF  GRID  USED 

FO^NON-INDUCTIVE  RESIST- 


SINGIE-RAIL   SYSTEM  ' 

i;ig.  63  shows  a  typical  alternating- 
current  traek  circuit  using  the  single-rail 
scheme,  and  its  relation  to  the  propulsion 
system.  As  practically  all  of  the  propul- 

rail  within  the  distance,  D,  the  length  of 
the  block,  and  relatively  little  through  the  block  rail,  there  will  be.  a 
drop  in  voltage  in  the  former  and  not  in  the  latter.  This  drop  ap- 
pears at  A  and  at  B,  the  sum,  of  which  will  equal  D.  Thus  a  small 
amount  of  propulsion  current  will  flow 
through  a  track  relay  at  one  end  of 
the  section  and  through  the  secondary 
of  the  track  transformer  at  the  other, 
the  effect  of  which  is  to  magnetize  the 
iron  of  each  to  a  certain  extent  and,  if 
excessive,  to  diminish  the  influence  of 
the  alternating  signal  current.  In  or- 
der to  limit  this  effect  of  the  propul- 
sion current  on  the  relay,  a  non-in- 
ductive resistance,  Pjgp6<$  is  connected 
in  series  with  the  relay  and  a  react- 
ance, KilfZdS1,  of  low  ohmic  resistance 
in  multiple  with  the  relay.  In  like 

manner  the  track  transformer,  Fig.  66,    FIG-  65~Low  RESISTANCE  IMPED- 
is  protected  by  a  non-inductive  resist- 
ance in  series  with  it.     As  a  further  precaution  against  the  magnet- 
izing effect  of  the  propulsion  current,  the  iron  of  both  transformer 
and  reactance  coil  is  provided  with  an  air  gap.     In  case  of  a  short- 


RAILWAY  SIGNALING 


circuit  between  the  power  and  block  rails,  fuses  protect  the  appara- 
tus from  injury.  The  resistance  in  circuit  with  the  transformer 
secondary  serves  the  further  purpose  of  limiting  the  flow  of  alter- 
nating current  when  the  rails  are  short-circuited  by  a  train. 

The  type  of  alternating-current  relay  used  with  the  single-rail 
scheme  *& -shown  in  Figs.  67  and  68  and  consists  of  a  movable  alumi- 
num disc  or  section  of  a  disc  passing  between  the  poles  of  a  magnet. 
A  part  of  the  pole  faces  are  enclosed  by  a  closed  conductor  thus 
causing  a  distorted  field  which  by  the  repulsion  between  it  and  the 
field  set  up  by  the  eddy  currents  induced  in  the  disc  causes  the  nec- 
essary mechanical  movement  of  the  disc.  The  shaft  upon  which 

this  disc  is  mounted  carries  contact  parts 
(at  a  short  radius)  which  operate  to  con- 
trol other  circuits  which  operate  the  sig- 
nals. 

When  a  block  is  not  occupied  by  a 
train,  the  drop  in  propulsion  voltage  D 
(see  Fig.  63)  is  divided  between  A  and  B 
in  proportion  to  the  ohmic  resistance  of 
the  apparatus  connected  across  the  rails 
at  those  points,  the  drop  in  the  block  rail 
being  relatively  negligible.  This  is  the 
case  also  when  a  train  is  in  the  middle  of 
the  block.  When,  however,  a  train  is  at 
A,  both  the  block  and  return  rail  are  at 
the  same  potential  at  that  point  because 

connected  by  the  wheels  and  axles,  which  also  shunt  the  relay.  Drop 
D  now  appears  at  B,  thus  creating  perhaps  the  most  unfavorable 
condition  for  the  transformer,  for  it  now  receives  the  maximum 
direct  current  from  the  track  while  delivering  an  increased  amount 
of  alternating-current.  When  a  train  is  at  B  the  transformer  re- 
ceives no  direct  current  and  delivers  the  maximum  alternating  cur- 
rent. Simultaneously  the  relay  receives  direct  current  due  to  the 
total  drop  D,  and  ?t  would  not  matter  if  its  iron  were  saturated,  for 
alternating  current  is  not  present  because  a  train  occupies  the  block, 
hence  the  relay  is  properly  inoperative  and  the  signal  indicates  dan- 
ger. 

The  means  provided  to  protect  the  track  transformer  and  relay 
from  the  effect  of  the  propulsion  direct-current  drop,  limits  to  some 
extent  the  useful  effect  of  the  alternating-current  in  the  track  cir- 


FIG.   66 — TRACK  TRANSFORM- 
ER   WITHOUT    CASE 


RAILWAY  SIGNALING  91 

cuit.  Clearly  then  there  is  a  limit  to  the  amount  of  direct-current 
drop  under  which  an  alternating-current  track  circuit  of  given 
length  will  be  operative  with  the  single-rail  scheme.  Fortunately 
this  point  has  not  been  reached  in  practice,  for  a  loss  of  energy  in  a 
rail  return  system  sufficient  to  disable  the  alternating-currfht  track 
circuit  could  not  ordinarily  be  tolerated. 

In  the  single-rail  scheme  the  amount  of  alternating  signal  cus- 
rent  in  the  track  rails  is  relatively  small  so  that  its  drop  in  voltage 
between  the  transformer  and  relay  is  not  serious.  The  insulation 
resistance  between  the  block  rail  and  return  rail  is  another  factor 


FIG.     67— ALTERNATING-CURRENT    RELAY        FIG.     68— RELAY     WITH     BASE     REMOVED, 
WITH     GLASS     COVER     REMOVED  SHOWING    MOVABLE    VANE 

greatly  affecting  the  operation  of  the  track  circuit.  Not  only  does 
this  decrease  as  the  length  increases,  but  it  varies  greatly  with 
weather  and  other  conditions.  The  expedient  of  increasing  the 
transformer  capacity  to  overcome  leakage  difficulties  (occasionally 
as  low  as  two  ohms  per  thousand  feet  of  track)  is  not  wholly  ad- 
vantageous because  increasing  the  alternating-current  track  voltage 
at  the  transformer  increases  in  like  proportion  the  leakage  current 
from  block  to  the  return  rail,  and  it  increases  the  alternating-cur- 
rent drop  in  the  rail  because  of  this  increased  current,  so  that  the 
relay  is  not  greatly  benefited.  It  is  better  to  reduce  the  length  of 
the  track  circuit  where  necessary,  as  that  is  more  beneficial  in  every 
way.  This  does  not  necessarily  mean  that  the  block  must  be  short- 
ened for  the  track  between  the  signals  may  be  subdivided  into  a 
number  of  track  circuits,  each  one  of  which  controls  the  signal.  It 
may  be  seen  that  the  signaling  equipment  is  in  a  sense  a  compromise 


92  RAILWAY  SIGNALING 

with  respect  to  a  number  of  conditions  which  are  conflicting  and 
which  to  some  extent  cannot  be  known  in  advance.  Experience 
thus  far  has  not  presented  track  conditions  requiring  more  than  one 
track  circuit  between  signals.  A  number  have  been  in  service  more 
than  three  years  which  are  about  one  mile  in  length  and  give  no 
trouble. 

APPLICATION    OF   THE   SINGLE-RAIL,   SYSTEM 

The  most  notable  installation  in  which  the  single-rail  alternat- 
ing-current track  circuit  is  used  is  that  of  the  New  York  Subway. 
In  this  the  automatic  block  signals,  Figs.  69  and  70,  automatic  train 
stops,  Fig.  71,  and  interlocking  switch  and  signal  plants,  (the  latter 


FIG.  69 — FRONT  VIEW  OF  A  TYPICAL  BLOCK  SIGNAL 
IN   THE   NEW   YORK    SUBWAY 

signals  being  semi-automatic)  are  of  the  electro-pneumatic  type. 
The  track  relay  control  circuits  which  in  turn,  control  magnetically 
operated  pin  valves  governing  the  admission  of  air  to  the  cylinders 
which  actuate  the  signals  and  train  stops.  In  this  installation  the 
two  alternating-current  signal  mains  carry  current  at  500  volts  and 
60  cycles.  To  these  mains  are  connected  the  primary  leads  of  the 
track  circuit  transformers  which  step  down  by  one  secondary  wind- 
ing to  ten  volts  for  supplying  the  track  circuit,  and  by  another  sec- 
ondary winding  to  55  volts  for  the  signal  lights.  The  non-inductive 
resistance  of  one  ohm  between  the  track  rails  and  the  ten-volt  sec- 


RAILWAY  SIGNALING 


93 


ondary  causes  a  drop  of  about  two  and  one-half  volts,  so  that  the 
alternating-current  potential  across  the  rails  opposite  the  trans- 
former is  seven  and  one-half  volts.  A  similar  resistance  in  series 
with  the  alternating-current  track  relay  at  the  opposite  end  of  the 
block  causes  an  additional  drop  of  two  volts,  reducing  the  voltage 
of  the  relay  to  about  five  volts  which  allows  one-half  a  volt  for  drop 
in  the  rails.  These  values  are  only  approximate. 

The  alternating-current  energy  required  per  block  may  be 
summed  up  as  follows :  That  for  the  signal  lights,  the  one  ohm  re- 
sistances and  the  leakage  (from  rail  to  rail),  non-inductive,  and  that 

for  the  track  transformer,  the 
impedance  of  the  rails,  the  track 
relay  and  the  impedance  coil  con- 
nected across  the  relay  terminals, 
partially  inductive.  The  power- 
factor  of  the  whole  is  about  80 
percent  and  the  load  per  average 
block  with  average  traffic,  80 
watts. 

In  order  to  secure  the  greatest 
safety  as  well  as  density  of  traf- 
fic on  the  express  tracks  .and  at 
curves  on  the  local  tracks,  the 
signals  were  placed  at  intervals 
as  close  as  the  braking  distance 
of  a  train  plus  a  reasonable  mar- 
gin of  safety  would  permit.  The 
element  of  personal  error  on  the 
part  of  the  motorman  was  elimi- 
nated by  the  automatic  stops, 
Fig.  10,  which  apply  the  brakes 
when  he  fails  to  observe  a  dan- 
ger indication  of  the  signal.  It 
has  been  found,  however,  that 
the  moral  effect  of  this  train  stop 
is  very  great,  for  no  motorman 
will  carelessly  invite  the  censure  of  his  employers  and  the  public 


FIG.   7O — SIGNAL  APPARATUS — REAR 
VIEW* 


*This  figure  shows  the  details  of  the  alternating-current  signals  as  ap- 
plied to  the  Subway  in  New  York.  The  track  transformer  is  at  the  top. 
Beneath  it  is  the  instrument  case  containing  the  grid  resistances,  track  re- 
lay and  reactance  coil.  Below  the  case  is  the  electro-pneumatic  valve  for 
controlling  the  automatic  train  stop. 


94 


RAILWAY  SIGNALING 


by  a  non-observance  of  the  signal  thus  made  conspicuous  by  the 
noise  of  escaping  air  and  the  sudden  stoppage  of  the  train. 

In  such  a  case,  the  only  question  of  veracity  at  issue  is  whether 
the  stop  was  in  the  danger  position  while  the  signal  indicated  safety, 
a  situation  which  exists  when  some  part  of  the  stop  mechanism  or 
its  controlling  circuits  are  deranged.  To  avoid  serious  delay  to 
traffic  when  the  stop  apparatus  is  out  of  order,  means  are  provided 
whereby  a  guard  may  hold  the  stop  in  the  clear  position  while  his 
train  pulls  over  it,  but  as  soon  as  this  act  of  the  guard  ceases  the 
stop  returns  to  the  danger  position. 

The  remarkable  record  of  performance  of  the  signal  system  in 
the  New  York  Subway  is  worth  noting.  The  failures  due  to  all 

causes,  many  of  which 
are  not  directly 
chargeable  to  the  sig- 
nal apparatus,  are 
about  one  to  every 
400000  signal  opera- 
tions. Some  months 
it  is  not  so  good  while 
in  others  it  is  even 
better. 

ALTERNATING  -  CUR- 
RENT SIGNALING  ON 
STEAM   ROADS 

Recent  develop- 
ments  indicate  that  al- 
ternating-current sig- 
naling will  have  a 
large  field  on  steam  roads.  This  is  primarily  due  to  the  trouble  ex- 
perienced with  foreign  direct  currents,  chiefly  from  trolley  cars, 
which  interfere  with  the  battery  current  commonly  used  in  the  track 
circuit.  For  this  purpose  alternating  current  at  a  frequency  of  25 
cycles  is  most  desirable  because  of  the  relatively  low  impedance  in 
the  line  wires  and  track  rails  due  to  reactance.  No  inductive  bonds 
at  the  ends  of  the  track  circuits  are  required;  hence  the  necessary 
alternating  current  in  the  rails  is  limited  to  the  needs  of  the  track 
relay  and  leakage  from  rail  to  rail.  By  the  use  of  a  relay  of  special 
design  requiring  a  very  small  amount  of  current  to  operate,  the  total 
current  in  the  rails  is  so  small  as  to  cause  but  little  drop,  which  per- 
mits of  the  use  of  a  long  track  circuit. 


FIG.   71 — DWARF   SIGNAL  AND  AUTOMATIC  TRAIN 
STOP 


RAILWAY  SIGNALING  95 

Alternating-current  signaling  on  steam  mads  lends  itself  read- 
ily to  the  wireless  control  of  distant  signals,  without  the  use  of  per- 
manent magnets  and  the  danger  of  residual  magnetism. 

In  this  connection,  it  should  be  noted  that  with  the  alternating- 
current  relay  the  shunting  voltage  is  practically  the  same  as  the 
pick-up  voltage.  Incidental  but  important  advantages  of  the  use  of 
the  alternating-current  for  signaling  steam  roads  are  that  the  signals 
may  be  operated  and  lighted  by  alternating-current  taken  from  the 
mains  which  supply  the  track  circuit.  Thus  all  batteries  are  elimi- 
nated as  well  as  oil  for  the  lights  and  the  services  of  lampmen. 

One  two  candle-power,  four  and  one-half  watt  lamp  per  sig- 
nal blade  gives  better  illumination  than  the  average  oil  light  and  it 

does  not  smoke  the  lenses  nor 
blow  out.  The  lights  may  be  al- 
lowed to  burn  continuously  night 
and  clay,  as  it  ordinarily  would 
not  pay  to  turn  them  off  because 
of  the  small  energy  required  and 

•P""*^}  the  long  life  of  such  lamps.   The 

signals  may  be  operated  by  in- 
duction motors  (having  neither 

FIG.  72— DETAILS  OF  AUTOMATIC  TRAIN      brushes   nor   commutators)    and 

the  slot  magnets  likewise  may  be 
operated  with  alternating  current. 

The  foregoing  considerations,  in  addition  to  the  chief  advantage 
of  non-interference  of  foreign  current  in  the  track  circuit,  are  all  in 
favor  of  alternating  instead  of  direct-current  operation.  The  weak- 
ness of  the  alternating-current  system,  however,  lies  in  the  possi- 
bility of  disabling  a  number  of  signals  due  to  breakage  or  crosses 
of  the  two  wires  constituting  the  signal  supply  mains. 

High  voltage  wires  are  not  desirable  on  telegraph  pole  lines, 
but  if  conditions  permit  the  use  of  low  voltage,  say  500  volts,  they 
may  be  placed  on  poles  with  other  wires,  but  should  be  on  the  top 
cross-arm,  so  that  other  wires,  which  break  more  readily,  may  not 
fall  upon  and  cross  them.  A  good  arrangement  is  to  have  an  inde- 
pendent pole  line  for  the  signal  mains  if  a  high-tension  pole 
line  is  not  available,  and  make  the  construction  so  substantial  that  it 
will  not  break  down.  The  stations  supplying  current  to  the  mains 
should  be  equipped  with  apparatus  in  duplicate.  By  thus  treating 
the  equipment  which  is  common  to  a  number  of  signals  with  the 
same  care  that  is  bestowed  upon  electric  power  and  lighting  sys- 
tems, this  part  of  the  signal  system  could  be  made  reasonably  reliable. 


CHAPTER  VIII 

AUTOMATIC  BLOCK  SIGNALING— ALTERNATING  CURRENT 

DOUBLE-RAIL  RETURN  SYSTEM 
DIRECT-CURRENT   TRAIN    PROPULSION 

SIGNALING  by  the  double-rail  return  system,  in  which  both 
rails  are  used  as  return  conductors  for  the  train  propulsion 
current  simultaneously  with  the  alternating-current  block  sig- 
naling current,  is  accomplished   by  the  use  of  balanced   inductive 
bonds  connected  across  the  rail  insulations  at  the  ends  of  the  blocks. 
These  bonds  offer  impedance  to  the  passage  of  the  signaling  current, 
but  not  to  an  appreciable  extent  to  the  passage  of  the  return  train 
propulsion  current.  1   A  good  form  of  reactance  bond  is  that  shown 


roDcy  or    i  nird  Rail 


A.C.  Signal 
Generator 

FIG.    73 — TRACK    AND    SIGNAL    CIRCUITS 

The  dotted  and  full  line  arrows  show  the  direction  of  the  alter- 
nating and  direct  currents  respectively. 

in  Fig.  73,  in  which  the  propulsion  current  passes  from  the  rails  into 
the  ends  of  the  coil  at  A  and  B  and  out  at  C,  the  middle  of  the  coil 
of  the  bond,  or  in  at  the  middle  at  D  and  out  at  the  ends  E  and  F. 
With  equal  amounts  of  return  current  in  each  rail  the  magnetizing 
effect  on  the  iron  is  nil,  but  the  signaling  current,  which  flows  from 
end  to  end  of  the  bond  (A  to  B),  sets  up  a  reactance,  which  main- 
tains a  difference  of  potential  between  the  rails  sufficient  to  operate 
the  inductive  track  relay.  The  propulsion  current  is  shown  fey  full 
arrows  and  the  signaling  current  by  dotted  arrows.  Unlike  the  sin- 
gle-rail return  system,  the  drop  of  voltage  in  each  rail  due  to  the 


RAILWAY  SIGNALING  97 

propulsion  return  current  is,  under  favorable  conditions,  nearly 
equal,  so  that  little  or  no  propulsion  current  flows  through  the  track 
transformer  at  one  end  or  the  track  relay  at  the  other  end  of  the 
block.  For  this  reason  it  is  not  necessary  to  interpose  resistances 
between  the  track  and  this  apparatus,  nor  to  connect  an  inductive 
shunt  across  the  relay  coils.  The  iron  of  the  track  transformer  has 
a  closed  magnetic  circuit,  that  is,  it  is  without  an  air  gap. 

Adjustable  magnetic  leakage  filler  blocks  are  inserted  between 
the  primary  and  secondary  coils,  causing  a  drop  of  voltage  and 


FIG.    74 — INDUCTIVE  BONDS 

The  wooden  covers  are  removed  to  show  details  of  bonds. 

limiting  the  current  when  the  transformer  is  short-circuited  by  a  train 
in  the  block. 

It  is  probably  never  true  in  practice  that  equal  amounts  of  pro- 
pulsion current  are  carried  by  each  rail  of  a  block  owing  to  unequal 
resistance  due  to  defective  bonding  and  the  like.  The  difference 
in  the  amount  of  current  in  the  two  rails  is  called  unbalancing  cur- 
rent because  its  effect  on  the  iron  of  the  bond  is  not  neutralized  by 
an  equal  amount  of  current  through  the  opposite  half  of  the  bond. 

It  should  be  noted  here  that  a  bond  as  a  unit  consists  of  the  coil 
and  iron  within  a  cast  iron  case  included  between  A  and  B,  and  an- 


98  RAILWAY  SIGNALING 

other  like  bond  between  E  and  F.    The  middle  points  of  their  coils 
are  connected  by  a  conductor  C  D. 

Properly  the  inductive  bond  around  each  rail  insulation  consists 
of  one-half  of  each  bond  as  A  C  D  E  and  B  C  D  E. 

In  order  to  reduce  the  magnetizing  effect  of  the  unbalanced 
propulsion  current  on  the  bond  A  B  or  E  F  so  that  its  reactance  to 
the  alternating  signaling  current  will  undergo  but  little  change,  an 
air  gap  is  introduced  into  the  iron  of  the  bond.  Obviously,  the  re- 
luctance of  this  air  gap  considerably  reduces  the  reactance  to  the 
alternating  signaling  current,  thus  requiring  additional  signaling  cur- 
rent through  the  bond  to  maintain  the  necessary  difference  of  alter- 
nating-current potential  between  the  rails. 

TTThe  increased  current  required  by  the  bond  E  F  at.  the  relay 
end  of  the  block  causes  additional  alternating-current  drop  in  the 
rails,  which  in  turn  necessitates  a  higher  voltage  and  more  current 
from  the  track  transformer.  Thus  the  bond  A  B  at  the  transformer 


A.  C.  Mains 

J 

VVW  Track 
C  ^Inductive  Bonds             (^Transformer           _^*fcB 

T7?   !                                   ' 

Track                     j      9~p9 

wv  Relay  Exciting 
P  Transformer 

Relay   H 
Q 

1 

FIG.   75 

receives  more  current  than  it  otherwise  requires  in  order  that  the 
bond  E  F  at  the  relay  receive  enough  to  maintain  sufficient  voltage 
to  operate  the  track  relay.  Hence  the  signal  mains  must  have  suffi- 
cient copper  and  the  generating  plants  be  of  sufficient  capacity  to 
maintain  these  conditions. 

For  the  above  reasons  it  is  occasionally  desirable  to  locate  the 
track  transformer  in  the  middle  and  use  a  track  relay  at  each  end  of 
the  block,  or  an  equivalent,  and  in  some  respects  better  arrangement 
is  to  use  but  one  track  relay  having  wire-wound  field  and  armature 
and  energize  the  field  from  one  end  of  the  track  circuit  and  the  ar- 
mature from  the  other  through  a  small  step-up  transformer  and  line 
wires.  (See  Fig.  75.)  It  will  be  seen  that  the  design  of,  and  power 
required  for,  a  signal  system  depends  upon  the  kind  of  maintenance 
which  a  railroad  company  gives  the  return  conductors,  the  rails,  in  the 
way  of  bonding;  for  if  the  bonding  is  good,  with  a  resulting  equal 
amount  of  current  in  each  rail,  the  air  gap  in  the  bonds  may  be  made 


RAILWAY  SIGNALING 


99 


very  small.  Such  desirable  conditions  mean  a  saving  in  line  copper, 
capacity  of  generating  plant  and  operating  expenses,  or  if  conditions 
warrant  it,  a  considerable  increase  in  the  workable  length  of  track 
circuit.  Ordinarily  railroad  companies  are  not  willing  that  even 
very  defective  bonding  should  result  in  a  danger  signal  with  the  block 
unoccupied,  so  that  alternating-current  signal  plants  are  now,  and 
more  will  be,  in  service  in  which  the  inductive  bonds  have  unbalanc- 
ing capacities  equal  to  perhaps  one-half  or  more  of  the  total  propul- 
sion load.  The  importance  of  this  feature  is  perhaps  more  clearly 
seen  when  compared  with  the  simplicity  and  economy  of  the  single- 
rail  system  of  alternating-current  signaling  on  direct-current  roads, 


\l\JWVVfVV 


FIG.    76 — SIGNALS    ON   ELECTRIFIED   RAILROAD 

Inductive  bonds  are  shown  on  each  track  between  the  rails. 


and  especially  on  steam  roads.  In  this  connection  it  will  be  noted 
that  in  a  general  way,  the  double-rail  return  system  is  preferable  to 
the  single-rail  system  in  cases  where  the  blocks  are  long,  hence  re- 
quiring relatively  few  inductive  bonds,  and  where  the  running  rails 
are  the  sole  conductors  for  the  return  of  the  propulsion  current, 
whereas  the  single-rail  scheme  is  to  be  preferred  for  the  opposite 
conditions,  a  notable  illustration  of  which  is  the  Interbo rough  Rapid 
Transit  System  in  New  York  City. 

The  current  taken  by  the  track  relays  and  the  inductive  bonds, 
has  considerable  lag  owing  to  the  highly  inductive  nature  of  the  ap- 
paratus, while  that  which  leaks  from  rail  to  rail,  due  to  the  compara- 
tively low  resistance  of  the  ballast  and  ties,  has  a  power- factor  of 
unity. 


100 


RAILWAY  SIGNALING 


The  frequency  ordinarily  used  is  25  cycles.      The  track  relay 
is  of  the  induction  type  and  does  not  respond  to  direct  current. 

ALTERNATING-CURRENT 
V->-          PROPULSION 

I  The  double-rail  return 
system  of  alternating-cur- 
rent roads  is  very  similar 
to  that  for  direct-current 
roads,  except  that  the  in- 
ductive bonds  have  no  air 
gaps  and  are  of  smaller 
capacity,  and  the  track  re- 
lays are  of  a  somewhat  dif- 
ferent type. 

As  the  propulsion  cur- 
rent has  a  frequency  of 
25  cycles  or  less,  the  sig- 
naling current  is  given  a 
frequency  of  60  cycles  in 
order  that  a  track  relay 
may  be  used  which  re- 
sponds to  a  current  of  the 
latter  frequency  and  not  to 

the  former.  In  other  words,  the  relay  operates  selectively  on  fre- 
quency and,  of  course,  does  not  respond  to  any  foreign  direct 
current  which  may  be  present,  jf 

This  system  is  now  in  service  on  the  New  York,  New  Haven 
and  Hartford  railroad,  and  gives  satisfactory  results. 


FIG.   77 — TRANSFORMERS 

Used  to  step  down  voltage  from 
high  tension  signal  mains  to  low 
voltage  signal  circuits. 


CHAPTER  IX 


GREEN  ffi  YELLOW  •  BLACK 


THE  LANGUAGE  OF  FIXED  SIGNALS 

THE  previous  chapters  have  dealt  with  the  principle^  and  with 
the  actual  details  of  the  apparatus  used  in  operating  the  vari- 
ous forms  of  signal  apparatus.    To  the  railway  employes,  to 
the  passengers  and  to  the  casual  observer  the  signal  indications  them- 
selves are  the  important  features  of  a  signal  system.   The  actual  mech- 
anisms used  to  accomplish  the  desired  results  are  not  of  especial  in- 
terest so  long  as  they  give 
the  positive  indications  de- 
sired relative  to  the  condi- 
tion of  the  tracks  and  posi- 
tions of  trains.     Two  kinds 
of  indications  are  used,  one 
for  day  and  one  for  night 
service.       The     semaphore 
arm,   in   various  positions, 
is  used  in  the  daytime.     A 
light,    mounted    behind    a 
spectacle    attached    to    the 

STOP  PROCEED  CAUTION        PROCEED 

HOME    SIGNAL  DISTANT  SIGNAL 

FIG.     78 — ONE-ARM,    HIGH,    TWO-POSITION    IN- 
TERLOCKED TRACK   SIGNALS 


MEANINGS 

Home  Signal. 

Stop — Remain  stopped ;  route  is  not  ready 
for  train  to  proceed. 

Proceed — Route  is  ready  for  train  to  pro- 
ceed. 

Distant  Signal 

Caution — Prepare   to   stop  at  next  home 
signal. 

Proceed — Expect  to  find  next  home  sig- 
nal in  proceed  position. 


semaphore  and  holding  col- 
ored roundels  is  used  at 
night.  The  semaphore  sig- 
nal is  primarily  a  position 
signal,  yet  in  many  sys- 
tems the  shape  and  color  of 
the  signal  blade  must  also 
be  considered  in  order  to 
properly  interpret  the  vari- 
ous indications  displayed. 
The  oldest  and  most 


common  types  of  inter- 
locked track  signals  are  shown  in  Fig.  78.  The  two  semaphore  arms 
on  the  left  have  square  ends  and  are  painted  red  with  a  white  band 
near  the  end.  The  night  indications  show  a  red  light  when  the 
the  blade  is  horizontal  and  a  white  light  when  the  blade  is  inclined. 
The  semaphore  arms  on  the  right  are  called  distant  signals  and 
have  notched  ends.  They  are  painted  green  with  a  white  V-shaped 
band  near  the  end.  At  night,  with  the  blade  horizontal,  a  green  light 
would  appear  and  with  the  blade  inclined  a  white  light. 


SIGNALING 


For  many  years  red  and  green  have  been  used  on  railroads  to  in- 
dicate danger  and  caution,  yet  on  most  roads  they  still  paint  their 

signal  blades  these  colors 
and  then  educate  their 
trainmen  so  that  they  un- 
derstand that  it  is  the  po- 
sition of  the  blade  and  not 
its  color  which  really 
counts. 

If  only  two  positions  are 
used,  it  is  evident  that  in 
the  case  of  the  distant  sig- 
nal, the  blade  must  be 
painted  a  different  color  or 
have  a  different  shape,  or 
both,  in  order  that  its  day 


B 


STOP  PROCEED      A  PROCEED 

FIG.     79 — TWO-ARM,    HIGH,    TWO-POSITION    IN- 
TERLOCKED  HOME  TRACK   SIGNALS 
MEANINGS 

Stop— Remain  stopped;  no  routes  ready 
for  train  to  proceed. 

Proceed  "A"— Superior  route  is  ready  for 
train  to  proceed. 

Proceed  "£"— One  inferior  route  is  ready 
for  train  to  proceed. 


indications  may  be  distin- 
guished from  those  of  the 
home  signal. 

The  home  signal  shown 
in  Fig.  78  would  be  used  only  to  govern  movements  over  a  track  hav- 
ing no  facing  point  switches  

for  diverging  routes,  but  this  I  ^j 
track  may  have  one  or  more 
derails  or  trailing  switches, 
which  must  be  properly  set 
and  locked  before  the.  signal 
can  be  cleared. 

In  Fig.  79  are  shown  two- 
arm,  high,  two-position  inter- 
locked home  track  signals.  The 
blades  are  all  painted  red 
with  a  white  band,  and  the 
night  indications  are  either 
red  or  white,  depending  on 
whether  the  blades  are  hori- 


STOP 


PROCEED 
"A" 


PROCEED  PROCEED 

V  "c" 

FIG.    8O — THREE-ARM,    HIGH,   TWO-POSITION 

INTERLOCKED    HOME   TRACK    SIGNALS 

MEANINGS 

Stop — Remain     stopped;      no     routes 


is  ready  for 
train  to  proceed. 

Proceed  "B" — Second  main  route  is 
ready  for  train  to  proceed. 

Proceed  "C" — One  inferior  route  is 
ready  for  train  to  proceed. 


zontal  or  inclined.  These  sig- 
nals are  used  where  there  is 
one    superior   or    main    route 
and  two  or  more  inferior  or  branch  routes.     The  lower  arms  gov- 
ern movements  to  any  of  the  inferior  routes.     Many  roads  never 


RAILWAY  SIGNALING 


103 


use  more  than  two  arms  on  any  post,  although  there  may  be  more 
than  one  superior  route.     Some  roads  always  place  two  arms  on 

one  post  although  there  may 
be  no  diverging  routes.  This 
is  done  for  uniformity  and 
in  this  case  the  lower  arm 
would  be  immovable. 

In  Fig.  80  are  shown  the  in- 
dications obtainable  by  the 
use  of  three-arm  two-position 
interlocked  home  track  sig- 
nals. The  blades  are  all 
painted  red  with  white  bands, 


either    red    or    white.       This 
arrangement     of     signals 


and    one    or    more    inferior 
routes.     The  use  of  this  type 


STOP    PROCEED   STOP  PROCEED  PROCEED 

"A"          "A"        "B"        "B"        "c" 

FIG.  8 1 — ONE-  AND  TWO- ARM,  TWO-POSITION 
DWARF  INTERLOCKED  HOME  TRACK  SIG- 
NALS 

MEANINGS  ' 

Stop— Remain   stopped;    route   is  not      and  the  night  indications  are 
ready  for  train  to  proceed. 

Proceed  "A" — Route  is  ready  for  train 
to  proceed. 

Stop  "B"— Remain  stopped;  no  routes     should   be    employed    only    at 
are  ready  for  tram  to  proceed.  «•.-«.* 

Proceed  "B"— Superior  route  is  ready      the    junctions    of     two     main 
for  train  to  proceed. 

Proceed    "C" — One    inferior    route    is 
ready  for  train  to  proceed. 

of  signal  is  constantly  be- 
coming  less   frequent,   and  ( 
the  necessity  for  its  use  is 
met    by    another    develop- 
ment to  be  described  later. 
Dwarf  track  signals  are 
.used    on    main    tracks    to 
govern  movements   against 
.the    regular     direction    of 
traffic  and  on  other  tracks    STOP       PROCEED 
to  govern    all    movements.     HOME  SIGNAL 
The    different     indications 
of  one  and  two-arm  two- 
position  dwarf  signals  are 


CAUTION  PROCEED 

DISTANT  SIGNALS 


TWO-POSITION  INTERLOCKED  TRACK  SIGNALS 
MEANINGS 

Home  Signal 

,_.  Stop— Remain    stopped;    route   is    not 

shown    in    Fig.    8l.        Ihe     ready  for  train  to  proceed, 
blades     are     red     with     a        Proceed— Route  is  ready  for  train  to  pro- 
white  band   and  the  night  Distant  signals 
indications    either     red    or      .  Caution— Prepare  to  stop  at  next  home 

white.       Since     all     dwarf        Proceed—  Expect  to  find  next  home  sig- 
signals   govern    movements     nal  in  proceed  position, 
which  should  be  made  at  low  speed,  the  two-arm  type  is  very  seldom 
used.     However,  track  conditions  sometimes  require  their  use  in 


IO4 


RAILWAY  SIGNALING 


order  that  one  arm  may  be  used  to  govern  one  particularly  im- 
portant route  only. 

The  signals  shown  in  Fig.  82  are  the  equivalent  of  those  shown 
in  Fig.  78,  the  only  difference  being  that  the  sweep  of  the  arm  is  90 

•degrees  instead  of  60  degrees, 
and  the  blades  are  painted  a 
neutral  color,  such  as  yellow. 
Two  types  of  distant  signals 
have  been  used  as  shown.  The 
distant  blade  with  the  square 
end  was  the  first  consistent  de- 
velopment of  the  practice  of 
giving  both  home  and  distant 
signal  indications  distinctly 
without  any  regard  to  color  or 
shape  of  blade. 

The  types  of  signals  shown  in 
Fig.  83  are  the  equivalent  of 
those  shown  in  Fig.  79,  the  only 
difference  being  in  the  sweep  of 
the  arms  and  the  color  of  the 
blades. 

All  of  the  signals  just  described  indicate  only  the  condition  of 
the  tracks  as  far  as  the  position  of  interlocked  switches  and  derails 
is  concerned.  They  do  not  indicate  the  presence  of  trains  or  whether 
the  interlocked  cross-overs  and  turn-outs  are  so  constructed  that  the 
movements  over  them  can  be  safely  made  at  a  moderately  high  speed. 


STOP  PROCEED     A"          PROCEED     B 

FIG.     83 TWO-ARM,     HIGH,     OX)      DEGREE 

TRAVEL,  TWO-POSITION   INTERLOCKED 

HOME   TRACK   SIGNALS 

MEANINGS 

Stop — Remain  stopped;  no  routes 
are  ready  for  train  to  proceed. 

Proceed  "A" — Superior  route  is 
ready  for  train  to  proceed. 

Proceed  "B" — One  inferior  route  is 
ready  for  train  to  proceed. 


RAILWAY  SIGNALING 


105 


Block  signals  are  used  to  indicate  the  presence  or  absence  of 
trains  between  definite  points.    Automatic  block  signals  usually  indi- 
cate more  than  this  because,  in  addition  to  the  other  meanings,  they 
indicate  the  condition  of  the  track  as  far  as  broken  rails  or  mis- 
placed switches  are  concerned. 

d_.^—         MIIINII  I  •       During     the    past    few    years 

when  the  railroads  have  been 
having  so  much  trouble  on 
account  of  broken  rails,  auto- 
matic block  signals  have  been 
a  great  protection.  On  one 
road  as  many  as  a  dozen 
cases  of  broken  rails  in  one 
month  were  indicated  by  their 
automatic  block  signals  and 
serious  wrecks  were  doubtless 


PROCEED         STOP  PROCEED         CAUTION 

HOME    SIGNAL  DISTANT    SIGNAL 

FIG    g^ — ONE-ARM,    HIGH,    TWO-POSITION  prevented. 

AUTOMATIC    HOME    AND    DISTANT    BLOCK 
SIGNALS 

MEANINGS 

Home  Signals 

Proceed — Block   is  in   condition 
for  train  to  proceed. _ 

Stop — Stop  and  wait  prescribed 
time,    then    proceed    with    caution, 
expecting   to   find   train   in   block, 
misplaced  switch  or  broken  rail. 
Distant  Signal 

Proceed — Expect    to    find    next 
home  signal  in  proceed  posititon. 

Caution — Prepare  .  to     stop     at 
next  home  signal. 

block  signals  of  the  one-arm 
type  shown  by  Fig.  84  cannot 
be  distinguished  from  the  in- 
terlocked signals  such  as 
those  shown  in  Fig.  78,  al- 
though their  meaning  is  dif- 
ferent. This  similarity  has 
caused  some  roads  to  place  a 
marker,  such  as  an  illumi- 


In  appearance  automatic 


PROCEED  STOP  PROCEED        STOP 

"A"     "B"  "A"    "B" 

FIG.  85 — TWO  -  ARM,  HIGH,  TWO-POSITION 
AND  ONE-ARM,  HIGH,  THREE-POSITION 
AUTOMATIC  HOME  AND  DISTANT  BLOCK 
SIGNALS 

MEANINGS 

Proceed  "A" — Block  is  in  condition 
for  train  to  proceed.  Expect  to  find 
next  home  signal  in  proceed  position. 

Proceed  "B" — Block  is  in  condition 
for  train  to  proceed.  Prepare  to  stop, 
at  next  home  signal. 

Stop— Stop  and  wait  prescribed  time,, 
then  proceed  with  caution  expecting  to* 
find  train  in  block,  misplaced  switch  or 
broken  rail. 


io6 


RAILWAY  SIGNALING 


iiated  letter  A,  on  each  of  their  automatic  block  signal  masts,  so  that 
when  an  engineer  comes  to  a  stop  signal,  he  can,  after  making  the 
stop,  readily  distinguish  between  the  interlocking  and  block  signals. 
Later  developments  in  the  art  have  led  to  further  refinements  in 

i  ^  i ' this  particular. 

The  home  and  distant 
signals  on  separate  posts  are 
used  in  overlap  block  systems, 
in  single  track  block  systems 
and  in  double  track  block  sys- 
tems where  the  blocks  are 
unusually  long. 

Automatic  signals  are 
more  commonly  used  on 
double  track  roads  with  heavy 
traffic  and  the  blocks  are 
short,  so  that  the  home  and 
frequently 


^    £JES 


STOP 


PROCEED         PROCEED  PROCEED 

"A"  "B"  "C" 

FIG.    86 — THREE- ARM,  TWO-POSITION    INTER-      , .  . 

LOCKED  HOME  TRACK  AND  SPEED  SIGNALS 


MEANINGS 

Stop — Remain      stopped. 


No 


« 


routes  are  ready  for  train  to  pro- 
ceed. 

Proceed  "A"—K  high  speed 
route  is  ready  for  train  to  pro- 
ceed. 

Proceed  "B" — A  moderate  speed 
route  is  ready  for  train  to  pro- 
ceed. 

Proceed  "C" — A  low  speed  route 
is  ready  for  train  to  proceed. 

mounted  on  the  same  post  or 

the   equivalent  three   position     CAUTION 

signal    shown    in    Fig.    85,    is 

used. 

All  of  the  signals  pre- 
viously described  are  types  in 
common  use.  They  have  not, 
however,  been  found  adequate 
for  the  conditions  which  have 
recently  been  arising.  It  has 
been  found  necessary  to  increase  the  capacity  of  roads  by  getting 
the  trains  over  them  faster.  High  speed  turnouts  and  crossovers 
have  been  put  in,  so  that  this  can  be  accomplished.  On  one  road  it  is 
•quite  common  practice  to  put  in  a  crossover  on  each  side  of  a  sub- 


PROCEED  PROCEED 

"A"  "B" 

FIG.  87 — TWO-ARM,  HIGH,  TWO-POSITION 
INTERLOCKED  DISTANT  TRACK  AND  SPEED 
SIGNALS 

MEANINGS 

Caution — Prepare  to  stop  at  next  home 
signal. 

Proceed  "A" — Expect  to  find  next  high 
speed  home  signal  in  proceed  position. 

Proceed  "B" — Expect  to  find  next 
moderate  speed  home  signal  in  proceed 
position. 


RAILWAY  SIGNALING 


107 


urban  passenger  station,  so  that  while  a  local  train  is  making  the  sta- 

tion stop,  an  express  can  come  up  behind  and  run  around  it  at  a 

speed  of  forty  miles  per  hour. 

Since  many  turnouts  cannot  be  taken  at  even  moderately  high 

speeds,  a  new  requirement  is  that  interlocked  signals  shall  also  indi- 

cate speed  as  well  as 
tracks  and  hence  the  de- 
velopment shown  in  Fig. 
86.  These  signals  require 
the  corresponding  distant 
signals  shown  in  Fig.  87. 
A  further  require- 
ment is  that  interlocked 
signals  shall  also  indicate 
the  condition  of  the  block 


i      i 


as  well  as  the  tracks  and 

Stop      Prot-eed    Proceed    Proceed      Proceed    Proceed        Proceed 

"A"     "B-      "C"     "D"     "E"      "F"        speed.    This  led  to  the  de- 

FIG.    88  -  THREE-ARM,     HIGH,    QO    DEGREE    UPWARD 
TRAVEL,  THREE-POSITION  INTERLOCKED  TRACK, 
SPEED   AND  BLOCK   SIGNALS 


. 
VClOpment     ShOWn     in    b  Ig. 

88.          At      prCSCllt      this      IS 


MEANINGS 

Stop — Remain  stopped.  Route  or 
block  not  ready  for  train  to  proceed. 

Proceed  "A" — Proceed  on  high 
speed  track.  Prepare  to  stop  at  next 
home  signal. 

Proceed  "B" — Proceed  on  high 
speed  track.  Expect  to  find  next 
home  signal  in  proceed  position. 

Proceed  "C" — Proceed  on  moder- 
ate speed,  track.  Prepare  to  stop  at 
next  home  signal. 

Proceed  "D" — Proceed  on  moder- 
ate speed  track.  Expect  to  find  next 
home  signal  in  proceed  position. 

Proceed  "E" — Proceed  with  ex- 
treme caution  on  low  speed  track. 

Proceed  "F" — Proceed  on  low 
speed  track. 

being  used  on  only  one  road, 
but  is  being  seriously  con- 
sidered for  general  adoption 
by  other  leading  roads.  This 
scheme  also  provides  for  a 
distinguishing  feature  between 
automatic  block  and  interlocked 
signals. 


PROCEED      PROCEED      PROCEED         STOP 
"A"  "B"  "C" 

FIG.  89 — TWO-ARM,  HIGH,  QO  DEGREE 
UPWARD  TRAVEL,  THREE-POSITION 
AUTOMATIC  BLOCK  AND  INTERLOCK- 
ING DISTANT  SIGNALS 

MEANINGS 

Proceed  "A" — Proceed.  Expect  to 
find  next  high-speed  home  signal  in 
caution  or  proceed  position. 

Proceed  "B"— Proceed.  Prepare 
to  stop  at  next  home  signal. 

Proceed  "C"— Proceed.  Expect  to 
find  next  moderate-speed  home  sig- 
nal in  caution  or  proceed  position. 

Stop — Stop  and  wait  the  prescribed 
time,  then  proceed  with  caution  ex- 
pecting to  find  train  in  block,  mis- 
placed switch  or  broken  rail. 


io8  RAILWAY  SIGNALING 

All  interlocked  signals  have  the  arms  and  lights,  one  ver- 
tically below  another,  while  the  automatic  block  signals  have 
the  arms  and  lights  staggered  as  shown  in  Fig.  89.  On  approaching 
an  interlocking,  the  block  signals  are  also  used  as  distant  signals  for 
the  interlocking  home  signals.  Where  the  block  indication  only  is 
given,  the  lower  arm  is  fixed  in  the  horizontal  position  and  is  really 
only  a  marker. 


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APR  15  1939 
181942  U 


CO 
DECS    1960 


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